Energy Optimization of Radio
NGR Micro G1 B2/25
Authors: Kasper Ornstein Mecklenburg &
Anton Blomgren
2016
Master´s Thesis
Electrical Measurements
Faculty of Engineering LTH
Department of Biomedical Engineering
Supervisor: Jonas Bengtsson & Johan Nilsson
Company: Ericsson
Energy Optimization of NGR Micro G1 B2/B25
Anton Blomgren &
Kasper Ornstein Mecklenburg
June 2016
1
Abstract
Rigorous studies have been conducted on Ericsson’s NGR
Micro G1 B2/B25 radio. The radio’s part in the telecommunications chain and components within the radio have
been determined and mapped according to certain characteristics giving an understanding of their function. The
obtained knowledge has been applied in order to make the
operation of the radio more energy efficient. This has been
done by implementing new sleep modes and improving already existing power saving features. The new sleep mode
Cell sleep, has taken the radio’s ”off state” from 32W to
18W. The features that have undergone revisions and have
been improved are TX micro sleep and MIMO sleep. In
short the features scale capacity depending on demand.
The original implementation of TX micro sleep consumed
44W with some additions to the feature this has been reduced to 38W and MIMO sleep has been reduced from 42W
to 39W. Combining the features gave a saving of 6W, from
38W to 32W.
2
Acknowledgements
During the process of this thesis we had to acquire knowledge within many different
fields and this was possible due to the people working at Ericsson, in Lund but also in
Lindholmen and Kista. We want to thank our supervisor Jonas Bengtsson for always
taking his time helping us and discussing various subjects, Per Sanderup for repairing
the radio when we broke it and for sharing his expertise in hardware, Ulf Morland for
help with SPI and clock measurements, Peter Nessrup for installing and showing how
the DU and radio software works, Robert Marklund for setting up an collaborative Latex
environment on local servers, Henrik Sundelin for tips on how to solder properly, Hans
Andersson for supplying us with radios, the staff on 4:4 for being helpful and making us
feel welcomed and finally the personnel at Lund Institute of Technology.
Anton Blomgren & Kasper Ornstein Mecklenburg
3
Contents
1 Introduction
6
2 Background theory
2.1 Telecommunications and 4G/LTE . .
2.1.1 Sites and traffic . . . . . . . .
2.1.2 FDD and TDD . . . . . . . .
2.1.3 Data transfer and bandwidth
2.2 NGR Micro G1 B2/B25 . . . . . . .
2.2.1 Downlink chain . . . . . . . .
2.2.2 Uplink chain . . . . . . . . .
2.3 Clocks . . . . . . . . . . . . . . . . .
2.4 DC/DC converters . . . . . . . . . .
2.4.1 Measurement theory . . . . .
2.5 Current power save methods . . . . .
2.5.1 Blocked cell . . . . . . . . . .
2.5.2 TX micro sleep . . . . . . . .
2.5.3 MIMO sleep . . . . . . . . . .
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3 Mapping the radio
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4 Methodology
4.1 Equipment and lab setup . . . . . . .
4.1.1 Radio NGR Micro G1 B2/B25
4.1.2 Measuring equipment . . . . .
4.1.3 UE . . . . . . . . . . . . . . . .
4.1.4 Control . . . . . . . . . . . . .
4.2 Minimum power consumption . . . . .
4.3 Buck dimensions . . . . . . . . . . . .
4.4 Potentiometers . . . . . . . . . . . . .
4.5 Possible applications . . . . . . . . . .
4.5.1 Cell sleep . . . . . . . . . . . .
4.5.2 TX micro sleep . . . . . . . . .
4.5.3 MIMO sleep . . . . . . . . . . .
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5 Results
5.1 Current radio energy consumption
5.1.1 Cell sleep . . . . . . . . . .
5.1.2 TX micro sleep . . . . . . .
5.1.3 MIMO sleep . . . . . . . . .
5.1.4 Feature combination . . . .
5.2 Buck dimensions . . . . . . . . . .
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25
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37
6 Discussion and conclusion
6.1 Buck dimensions . . . . . .
6.2 Cell sleep . . . . . . . . . .
6.3 TX micro sleep . . . . . . .
6.4 MIMO sleep . . . . . . . . .
6.5 Combined features . . . . .
6.6 Scalability . . . . . . . . . .
6.7 Hardware . . . . . . . . . .
6.8 Making the radio intelligent
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40
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4
7 Further work
46
8 References
46
9 Appendix
9.1 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48
48
5
1
Introduction
Scientists and researchers have proved that the modern way of life has many negative
effects on the climate and the environment. All over the world governments are adhering
to the facts and strive to reduce the impact that our way of life has on the planet. These
leaders are trying to establish national and international legislature in order to help the
transition to a more sustainable society.
In Sweden, for instance, the Ministry of the Environment has set up a number of goals
to reach by year 2020. The Ministry aims to have at least 50% of the consumed electricity produced from renewable energy sources and energy efficiency should increase
by at least 20%. The European Union has reached an agreement and set up goals to
increase energy efficiency by 20% by 2020 and to have 20% of the electricity originating
from renewable sources [1]. A part from governments, international organizations like
the UN and Greenpeace push for the establishment legislature and agreements in order
to hasten the transition towards a sustainable future. There is an increased pressure
on companies and institutions to adapt and become more sustainable, not only from
governments and organizations but also from the general public, as many become more
aware.
Many companies are seeing the benefits of a more sustainable way of business which
leads research and development towards new ideas and solutions. To optimize the use of
energy and utilization of resources is economically beneficial as well as making products
more attractive on the market. Some of the operators in Sweden claim to do their best
to minimize their impact on the environment and they have formulated goals of their
own. Tele2 for instance claim to make ”continuous efforts on reducing the energy consumption of the communication network” [2]. TeliaSonera has more concrete goals and
aim to reduce their energy consumption with 10% per subscription equivalent, meaning
that all their different services should use 10% less energy [3]. In Germany operators are
trying to become more sustainable by reducing their green house gas emissions through
energy optimization [4][5]. In Italy the same strive is proclaimed by some of the biggest
telecommunication operators [6][7][8]. All over the world there is an increased focus on
cost and energy consumption from operators. [9].
Ericsson is competing on the global market and today 40% of the worlds mobile traffic
passes through their networks [10]. They sell their services to operators around the
world and in order to keep their grasp on the market their products need to be very
competitive. There are many ways of having a competitive product for example; it can
be of the highest quality, have the best features or be the cheapest. With the pressure
of a more sustainable society from governments, legislation and the public, another aspect becomes increasingly important; the energy consumption of the product. With the
rapid technological evolution of modern society, a constant search for new products and
improvements has to be conducted in order for companies to stay in the forefront of the
market. This master thesis is such a search.
The master thesis strives to optimize and reduce the power consumption of Ericsson’s
radio NGR Micro G1 B2/B25. The radio together with a digital unit (DU) make up
the link between the users mobile phone or user equipment (UE) and the core network.
It is the link in a long chain which enables the connection to the World Wide Web. It
is also the part of the chain where most of the power is consumed, as can be seen in
Figure 1 80% of the energy in the chain is consumed in the radio access network (RAN)
[9].
6
Figure 1: Power consumption in the chain.
The RAN has the most opportunities of improvement, thus this thesis is focused on
the radio. The study is conducted on one of Ericsson’s smaller radios due to practical
reasons, a smaller radio has a lower output power and is therefore easier to handle. Less
caution needs to be taken and the output signal requires less attenuation. Ericsson’s
different radio models are quite similar and share many components and therefore optimization of the NGR Micro G1 B2/B25 is likely to be applicable on other models as
well. At the facility in Lund there is an advanced lab where simulations and real traffic
scenarios can be run. A lab environment very similar to the environment in real live
RAN was setup and traffic scenarios with actual UEs were run.
The research has been an iterative process and in this report the result of the first
iteration is presented as background theory. During the first iteration an understanding of the radio was acquired and the components were mapped and categorized. This
task has made up most of the research process and was extensive. Upon this ideas were
developed, applied and tested which make up the second iteration of the research process.
The report is divided into six sections. It begins with the background theory on which
the rest of the report is based and this section is vital for comprehension. Then the lab
setup and instruments used during the research are presented as well as our ideas of
improvement. This is followed by a presentation of the results of these ideas and then
concluded in discussion and conclusion. Subjects and ideas that were touched but not
finished are found under further work. At the end of the report the references are listed
as well as an appendix with necessary abbreviations.
7
2
Background theory
The purpose of this section is to supply the reader with all necessary information about
telecommunications with emphasis on long time evolution (LTE), how wireless data is
sent, theory on how to measure power correctly and methods Ericsson currently are
using to reduce power consumption in their radios.
2.1
Telecommunications and 4G/LTE
Ericsson’s LTE networks starts at the internet and ends with the wireless access point
created by the radio. It can be divided into four main parts:
• The core network which makes up the infrastructure of the network
• DU which controls the RAN
• Radios which transceives data
• UE enabling connection to the network.
The core network transports data between the servers of internet and out to the RAN.
The RAN made up of many cells where each cell consists of at least one radio and one
DU. There are two main categories of cells with different functions; the coverage cell
consists of a powerful radio which can cover large areas, the capacity cell which has a
smaller radio and covers a smaller area. The coverage cell supplies reception to a wide
area and hands over traffic to the capacity cell which is placed strategically at high traffic
areas to unload the coverage cell. The smaller cell is also used to supply reception to
areas where the larger coverage cell can not reach, for example in a subway station. In
Figure 2 the coverage cell can be seen covering a large area, the two smaller capacity
cells are seen covering smaller areas; a subway station and a square.
Figure 2: Example of application of the different cells.
8
The DU has the intelligence in the RAN and controls the radios, the communication
with the UEs and handles handovers between cells. It also handles all the administration of data, analysis and decision making, as well as interpreting data and handles
error control. It schedules the communication and decides which UEs talks and listens
to which frequency and when. The radio simply converts the digital data from the DU
to an analog signal and transmits it to the UEs and does the opposite in the other
direction. The UE allows the end user to interact with the network and connect to the
internet oblivious of the advanced technology behind it. In Figure 3 the chain from UE
to the world wide web can be seen, it also shows the communication from the UE to
the radio is refered to as uplink (UL) and from the radio to the UE as downlink (DL). [11]
Figure 3: Example of application of the different cells.
According to the LTE standard established by 3rd Generation Partnership Project
(3GPP) each cell has to send Cell-specific Reference signal (CRS) with each DL subframe. There are a number of other reference signals which has to be sent at certain
intervals in order to comply with the LTE 3GPP standard. This makes LTE quite
talkative because the radio sends out reference signals. [11]
2.1.1
Sites and traffic
The traffic going through different sites depends on their geographical location and also
what time of the day it is. During rush hour in a subway station the demand for capacity
is higher than at night. Figure 4 gives an overview how much traffic goes through sites.
The high traffic sites make out 10% of the sites and take 25% of all the traffic, 40% are
medium sites taking 60% of the traffic and finally 50% of all sites are low traffic site only
taking 15% of the traffic. The high traffic sites have a demand of at least 25% capacity,
the medium less than 25% and the low traffic sites down to no demand on capacity.
Half of the sites have long periods of just idling and waiting for users to make use of the
capacity available.
2.1.2
FDD and TDD
There are two different ways of communication in LTE; frequency division duplex (FDD)
and time division duplex (TDD) [12]. The principle for TDD (see Figure 5) is that
the radio and the UEs communicate on the same frequency but never at the same
time. In countries where bandwidth and frequencies are sparse TDD is more common.
TDD requires very high precision in time or else sending and receiving will overlap
9
Figure 4: How traffic is distributed on Ericsson’s sites.
creating noise and disturbance in the system. FDD (see Figure 6) is less prone to
disturbances as it sends and receives simultaneously due to that the radio and the UEs
always communicate on different frequencies. It is more expensive in bandwidth due to
that the bandwidth is split between sending and receiving. [11]
frequency
TDD principle
fdl,ul
RX
TX
RX
TX
RX
TX
time
Figure 5: Principle plot for TDD.
2.1.3
Data transfer and bandwidth
The transmission time interval (TTI) for LTE is 1 ms and every TTI consists of 14
symbols, i.e. a symbol is 1/14 ms or also 71.5 µs. During each symbol the radio has the
possibility to either transmit data or stay quiet. The amount of data sent during each
symbol depends on three parameters; load, modulation and available bandwidth.
Depending on the quality of the signal to the UE and radio different modulation can
be used. Basically, if there is good reception it allows for a high quality signal and the
transmitted data rate is high and vice versa. So when the signal is poor or when the
radio is signaling, QPSK is used and less data is transmitted. Higher modulated signals
are more sensitive to noise and disturbances. In Table 1 different modulations with
10
FDD principle
frequency
ful RX
fdl TX
time
Figure 6: Principle plot for FDD.
related bits can be seen.
Table 1: Modulations methods with related number of bits.
Modulation
BPSK
QPSK
16QAM
64QAM
256QAM
Bits per symbol
1
2
4
6
8
The general term for packaging data higher than one bit is in-phase/quadrature (I/Q)
data [13]. The principle is to use amplitude and phase to encode data onto a sine wave
as
A cos(2πfc t + φ) = A cos(2πfc t) cos(φ) − A sin(2πfc t) sin(φ)
where fc is the carrier frequency, t is time, φ is the phase and also
I = A cos(φ), Q = A sin(φ)
A reference sine wave of the same frequency is necessary in order to identify the phase
and amplitude of the modulated signal. Once I and Q have been determined they will
correspond to a certain coordinate in the complex plane. An example of a 16QAM 4bit
modulation scheme can be seen in Figure 7.
Apart from the modulation used, the bandwidth determines the data transfer rate.
LTE is defined for bandwidths of 1.4-20 MHz and the spacing between sub-carriers in
the bandwidth is 15 kHz [12]. A single sub-carrier during a symbol is referred to as a
resource element and an UE is assigned a certain number of elements creating a resource
block. A general formula to calculate the data transfer rate is defined as the number
of symbols per second times the bandwidth divided by 15kHz and finally multiplied by
11
Q, imaginary axis
16QAM
I, real axis
Figure 7: 16QAM 4 bit modulation scheme.
the bits which depend on the type of modulation used. A 20MHz bandwidth LTE radio
using 16QAM gives
20 · 106
· 4 ≈ 74.7M bit/s.
(1)
15 · 103
An important note is that this is the theoretical calculated value where all resource
elements are allocated to data transfer, however in practise some resource elements are
used for control and signaling to ensure that correct data has been received [14].
14 · 1000 ·
2.2
NGR Micro G1 B2/B25
The radio operates on band 2/25, which are two bands at similar frequencies used in
the USA. The frequencies span from 1930Mhz to 1995Mhz for downlink and 1850Mhz
to 1915MHz for uplink [15]. The Micro has a bandwidth of 20MHz and is capable of
64QAM modulation in downlink giving a maximum throughput of 150Mbit/s and in
uplink the bandwidth is 10Mhz and with a maximum of 16QAM modulation it has
50Mbit/s throughput. The radio uses a cavity filter which only lets desired frequencies pass through (bandpass filter) on both up- and downlink. It is connected to a DU
through an optic cable and communication is done through common radio protocol interface (CPRI).
The radio is designed to be used in a small cell, therefore it is smaller and has lower
output power level compared to the Macro radio which is used as a coverage cell. The
radio has two antennas and two sets of TX and RX chains (the RX chains share resources) in order to enable multiple output multiple input (MIMO) which allows for a
higher throughput. The output power of the Micro is 5W on each of the antennas, the
Macro has typically an output power of 40W per antenna. The two different radios have
similar hardware and some components are identical even though they have different
areas of application. Below follows a synoptic explanation of the downlink and uplink
chains inside the radio.
12
2.2.1
Downlink chain
The DU receives a data package from the core network. It decodes the recipient and
encodes the data to the same frequency as allocated to the UE, the packet is then sent
through the CPRI link to the radio. The radio receives the package and converts it
from a digital signal to an analog. It also converts the signal to the higher frequency
band of the radio, in other words it lifts the signal up to the carrier frequency. The
signal is then amplified in the power amplifier (PA) and in order to have the output
power specified by the DU, the signal from the PA is fed back for control to ensure that
the correct power level is met. The signal is now transmitted to the UE through one
of the antennas. The UE receives the package and if the error control is positive no
retransmission is necessary, otherwise the DU will resend the data and possibly change
to a lower modulation. [16]
2.2.2
Uplink chain
The UE sends a data package on a specific frequency assigned by the DU. The radio
receives the signal which is amplified in two stages before it is downconverted. In the
downconversion the carrier frequency is removed, the signal is converted down to lower
more manageable frequencies called intermediate frequency (IF). The signal is then
passed on to a analog to digital converter (ADC). The signal is now digital and in a
suitable format for the DU to which it is passed on for analysis and processing. If
necessary the DU will ask the UE to resend the data with an increased signal strength.
If the data is intelligible it is passed on to the core network and on to its destination.
[17]
2.3
Clocks
A clock is an oscillating circuit supplying an AC signal at a certain frequency. The
clocks drive the digital circuit, it is the pulse of the system. It supplies a mean for synchronization and drives the operation of the components. A clock can generate a signal
by sending a current through a crystal which then starts to vibrate and this vibration
decides the frequency of the clock signal. Some oscillators can vary the frequency of the
generated signal one example is the voltage controlled oscillator (VCO), where the input
voltage can adjust the generated frequency. These systems are often combined with a
phase locked loop (PLL) to synchronize the generated clock with a reference clock and
thereby the rest of the system. The PLL supplies feedback to the VCO which regulates
the clock frequency until the PLL has locked on to the reference clock. When a lock has
been established the clock signal is stable and in sync with the rest of the system. VCOs
are often used in components that need a higher frequency than the rest of the system,
if a lower frequency is needed instead a divider can be used. The divider reduces the
frequency by the integer chosen to divide it with. [18]
2.4
DC/DC converters
Buck converters are often used as an efficient mean of creating lower power domains
from higher voltage supplies. The converter is an analog device which rapidly switches
on and off, commonly a MOSFET transistor which creates a square wave. In order
to supply a steady voltage the square wave charges an inductor and capacitor when
high and when the square wave is low the inductor and capacitor discharge, creating a
smoother voltage. This creates ripple in the output voltage which is reduced by coupling
capacitors between supply and ground. Buck converters can be very efficient and some
13
achieve efficiencies of up to 95-96% [19]. The efficiency is dependent on a few fixed parameters and therefore they are designed to be used under specific conditions [20]. Once
the specific conditions have been set the efficiency curve depends on the current passing through the converter. One must therefore approximately know the power passing
through a power domain in order to choose appropriate parameters for a buck converter.
The buck converter has a small DC ripple which is hard to remove entirely, so when a
very consistent voltage supply is required a low-dropout (LDO) regulator is used instead.
The LDO regulator is a linear voltage regulator which supplies a very consistent and
ripple free voltage and is commonly used to supply for example VCOs. The efficiency of
a LDO is directly proportional to the input output ratio. If the input is 5V and output
is 3V the efficiency is 60%; a very wasteful converter compared to the buck. [21]
2.4.1
Measurement theory
To determine the current flowing through a circuit, the voltage drop over a resistor with
known resistance is measured. If the voltage has no reference to ground it is called a
differential measurement and using Ohm’s law the current is calculated according to
I = ∆U/R
(2)
where I is the current in A, ∆U the voltage drop in V and R the resistance in Ω. For this
equation to accurate results it is important that the measurement is done properly. In
Figure 8 the solderings avoid the contact resistance which is present between the PCB
and the resistor. This way of measuring the current is called a 4-pole measurement and
avoids the involvement of the contact resistance. This is due to that no current will pass
through the voltmeter and therefore the effects of the solderings are eliminated. The
power is finally calculated according to
P = U · I.
(3)
Figure 8: The grey area is the contact resistance between PCB and resistor, and the
black where the solders should placed to avoid measuring the contact resistance.
14
2.5
Current power save methods
There are some measures of power save functionality already available for the Micro and
other radios. Below follows a short description of the features that are implemented
today.
2.5.1
Blocked cell
When there is no traffic on a radio and it is known approximately when there will be
again the radio can be blocked. In this mode of operation the radio neither transmits
nor receives and it is for all intents and purposes switched off. Since it is known when
the radio needs to be up again boot time is no concern. [22]
2.5.2
TX micro sleep
The radio is not always transmitting, depending on the traffic and the scheduling of
the transmissions there will be windows in time when the radio is quiet. During these
windows the biasing to the final stage of the amplification is turned off. This is done
by generating a strobe signal based on information about the data to be sent from the
DU. The information is sent in a message which specifies at what symbols the radio is
to transmit during that TTI. This strobe signal toggles the biasing, turning it on and
off. [23]
2.5.3
MIMO sleep
When the traffic is low the full capacity of the radio is not needed. This allows for one
of the TX chains to be switched off. The throughput of the radio is thereby halved.
[24]
15
3
Mapping the radio
This part of the report have been removed due to confidentiality of Ericsson products.
In this part the inner workings of the radio is presented and this process was very time
consuming and made up a large portion of the research process.
16
4
Methodology
After going through the radio and its components in the first iteration, findings were
analyzed and possible applications of these findings were discussed and implemented.
In order to test and evaluate these findings a laboratory environment was setup. The
setup allowed for real traffic scenarios to be run on the actual equipment which makes
up the RAN in live networks. Below the lab setup and equipment is presented and after
that the possible applications established for the second iteration are introduced.
4.1
Equipment and lab setup
XYZ is a confidential component in the radio and its name has been changed.
4.1.1
Radio NGR Micro G1 B2/B25
In the lab setup a NGR Micro G1 for band 2/25 of version P1C running software with
Pid CXP9013268%9 R62SB01 has been used. It has been supplied with power from an
external source instead of the original power supply to give exact measurements of the
consumption of the radio without the losses of the initial power transformation. The
radio is open to enable direct access to the PCB. The PCB is attached to the bottom half
of the chassis which has a heatsink and the chassis is placed directly on the table. All of
the shields has been removed in order to be able to access components. It is cooled by
an external fan since the power consumption of the fan unit is not relevant for this study.
The opened radio is connected to its cavity filter through RF cables as shown in Figure
9. The filter in turn, is connected to a series of attenuators. Each branch is connected
to 20dB attenuators with a max effect of 50W. The radio’s peak effect makes it necessary to have an attenuator of that power level first in the series to avoid damaging
the equipment. Branch A is then connected to three smaller attenuators in series in the
following order: 10dB, 30dB and 10dB. Branch B was attenuated with two 20dB attenuators in series. It was unintentionally attenuated 10dB less however this did not affect
the results. The two RF cables then connect to splitters with another 10dB attenuation.
The splitters split the signals in to four which then is connected to four UEs. Figure 10
shows the lab setup and it is presented schematically in Figure 11. Note that the DU is
accessible through the local network.
In order to make detailed measurements a number of wires were soldered to certain
components and on to splines with pins glued to the side of the bottom half of the chassis. In Table 2 the resistors connected to the spline with pins for detailed measurement
of the DC/DC block are listed together with their power domain. The resistors were
chosen because they were easy to access and on the different power domains’ path.
Two wires were soldered on to each of the resistors, one before and one after the resistor
to allow for a differential measurement. This is all done in accordance to the 4 pole
measurement method. Connections were also made to certain signals of interest.
The radio is supplied by 36V through a modified RPM 777454/0200 cable. The cable
connector that connects to the original power supply (PSU) has been replaced by two
banana connectors.
For direct communication a testcard controlled through a program called Term-R4B25
was used. Moshell, an Ericsson internal command tool, is used to control a DU 4101
which in turn controlled the radio through the CPRI link. The CPRI link is connected
into the SFP A slot.
17
Figure 9: The opened radio connected to the cavity filter.
Figure 10: Lab setup.
Table 2: The resistors and their resistance, named as in the schematics [25].
Resistor
R337A10
R1003A10
R537A10
R534A10
R1215A10
R536A10
R643A10
R645A10
R646A10
R435A10
4.1.2
Resistance, mΩ
2.5
5
5
2.5
15
5
5
5
2.5
15
Power domain, V
5.1
Switch 5.1
3.7
3.3
3.0
1.8
1.35
0.982
0.768-0.877
16-32
Measuring equipment
The PSU used was an Agilent Technologies N6705B with dual power cells to supply 36V
and up to 3.5A and one of the other channels was used for measuring differential voltage
18
Figure 11: Schematics of the lab setup.
over the PA buck converter. For the measurements of the remaining buck converters a
National Instruments PXIe-1071 with two modules each with 8 differential measurement
channels was used. It has high sampling rates of up to 50MHz. The PXIe was controlled
by a computer running Ericssons own developed analysis tool, a labview program called
Power Analyzer v0.29. The PXIe has a max limit of voltage input (around 10V) even
though the voltage difference only is in order of mV over the resistors. Due to this
an Agilent 34401A multimeter was used for higher voltages, a Labview program was
written to gather data and control the instrument. To study clocks and other signals a
Yokogawa DL9240 oscilloscope was used together with Techtronic probes 10X, 10MΩ,
8.0pF and 500Mhz bandwidth.
4.1.3
UE
In order to simulate and test traffic on the radio, four UEs were used and can be seen in
Figure 12. The UEs were connected to a PC which runs the program LINS3 used to set
up the UEs. To simulate traffic data was sent and received from a server via Iperf3.0.11
win64 or online speed tests and general web browsing. The UEs were directly connected
to the radio through RF cables with attenuators connected, the signal strength perceived
by the UEs was approximately -80dB. The connection of four UEs enabled a maximum
load of the radio on both up- and downlink.
4.1.4
Control
Interaction to the radio was done through two different interfaces; the testcard with
debugging interface and the DU with the Moshell interface. Term-R4B25 was easy to
use and it was possible to create macros containing multiple commands. The testcard
also eliminated the need of CPRI communication which allowed turning off components
essential to the CPRI communication. The use of the DU with the Moshell interface
allowed for remote operation otherwise the two enabled the same internal control of the
radio. The features TX micro sleep and MIMO sleep were activated and deactivated via
the DU. The DU was running CXP102051/25 R7FJ with an added features enabling TX
19
Figure 12: Four UEs stacked on top of each other.
micro sleep and another enabling more advanced power measurements from the internal
supervision.
4.2
Minimum power consumption
After the first iteration the components’ function and how they were controlled had
been established. In order to get an idea of how much power could be saved by turning
off a component, putting it in standby or sleep mode the total power supplied to the
radio was measured while components were turned off, one after another. The radio
was in Blocked cell mode when conducting this study, it would otherwise reboot when
its circuits went offline. This essentially created a new more effective Blocked cell which
was named Cell sleep and represents the minimum power consumption of the radio while
still being rebootable via the CPRI interface.
4.3
Buck dimensions
After learning that the DC/DC block is similar to the one as in the much more powerful
Macro radio the dimensioning of the buck converters came into question. The buck converters are designed to work in specific conditions in order to be as effective as possible
and as the smaller radio consumes less power the buck converters might be dimensioned
incorrectly.
In order to justify the dimensions of the buck converters, a few tests were designed
to check their efficiency. By measuring the current going through resistors in Table 2
and the total current going in to the radio from the Agilent N6705B power supply an
estimate could be acquired. To measure the current passing through the resistor, and
thereby the buck converter, the voltage before and after the resistor and its resistance
needs to be known. The first 16 channels of the PXIe were then connected to the splines
on the side of the radio. The buck converter supplying the PA was connected to the
Agilent N6705B power supply channel B. The PA buck output voltage is adjustable and
20
is adjusted by the iWarp so in order to be able to conduct the calculations the voltage
source needs to be known, i.e. the voltage coming out of the converter. The voltage was
therefore measured by the Agilent 34401A multimeter.
To study the conditions the radio’s converters were working under a set of traffic load
scenarios were designed, they are presented in Table 3.
Table 3: Test traffic scenarios.
Name
Full
Half
Quarter
Ten
Idle
Blocked cell
Cell sleep
Total load
100%
50%
25%
10%
2%
0%
0%
To create the different scenarios four UE’s were used to send and receive data from a
server via Iperf, two sending and two receiving. The different loads were created by
taking the theoretical max throughput on both up- and downlink (50 and 150Mbit/s)
and dividing it with 2, 4, and 10. This gives the throughput for half, quarter and ten
percent load. Iperf was then configured to try to send and receive at those throughputs
for a certain amount of time. The Idle scenario was created by simply letting the UE’s
idle, no added traffic from Iperf, however the PC might have sent and received small
amounts of data. In the Blocked cell scenario the radio is not transmitting nor receiving
and in the Cell sleep scenario the new Blocked cell implementation is run.
The radio was connected to a computer through the testcard. The PSU was connected
to the same computer and the official software was used to collect data from the power
going in to the radio and the current through the PA buck. The sample rate of the PSU
was set to 1024 SPS. The multimeter was connected to the same computer and data
was setup to be collected at 3Hz. The sample rate of the PXIe was set to 10kHz and
before booting the radio it was calibrated to eliminate DC offset and just before the
first scenario it was calibrated in the regards of temperature. After booting the radio
the UEs was started and setup through LINS3 on the connected computer.
The traffic scenarios were run for 300 seconds from which 30 seconds of data was collected. Before the new scenario the PXIe was again calibrated in regards of temperature.
Iperf was taking too long to connect to be able to run the scripted scenarios so they had
to be run manually.
The conversion is done in steps, where in the conversion steps the measurement points
for where the DC/DC units were made can be seen as circles in Figure 13. By measuring
the power going in to the radio and what comes out after each step of conversion the
efficiency of each step can be estimated. The measurements were divided into three
according to the steps of conversion; the first the PSU, the second the PA and TRX
buck converters and the third the remaining buck converters and the 5.1V switch. So by
dividing the power measured after step two (total from all converters) and dividing it
with the power going in to the radio the efficiency of step to can be calculated. The same
approach gives the efficiency of step three but the power coming in to these converters
21
is the power coming out of the step two converters. The total efficiency was calculated
by dividing the power coming out of step three by the total power going in to the radio.
Due to accessibility it was not possible to measure before and after every individual buck
converter. This means that only the efficiency for the entire step can be calculated, not
for individual converters. Figure 14 is a picture of a resistor seen through a microscope
and makes a 4-pole measurement possible.
Figure 13: Circles show where the measurements of the power domains were done.
Figure 14: Solderings on a resistor used for a differential measurement.
The collected data was then imported to MatLab to be processed and analyzed. A low
pass filter was added when necessary to eliminate disturbances and make the data easier
to interpret.
4.4
Potentiometers
One idea was to continuously change the voltage to the two adjustable buck converters.
In order to do this the rise and settling time of the potentiometers voltage needed to
be known. The measurement was done by using the same measurement points as for
the differential measurement (R646A10 and R435A10) for the buck converters with the
difference that the measurement had a ground reference.
4.5
Possible applications
With the knowledge of the first iteration at hand, a search for possible applications was
initiated. A natural place to start was the already implemented features since it came to
22
be obvious that they could be improved. The features were studied more thoroughly and
additions to them was introduced and tested. A thorough presentation of the process
for the different features are presented below.
4.5.1
Cell sleep
The feature is only to be activated when the radio is not being used and it is known
when it again is needed. The idea was to simply reboot the radio at a preemptive time
with regards of the boot time. This means that the boot time of the radio is no concern
and the goal became to turn off as many components as possible while retaining communication via CPRI.
The earlier findings of minimum power consumption were reworked and some additions were made. The process was the same, turn off the component and study the
effect on the total power consumption, if CPRI communication is lost; take a step back.
4.5.2
TX micro sleep
In the current implementation only the biasing of the final amplification stage is turned
off and it is very fast, it has a very short response time, which is needed since the shortest time windows are 71.5µs (one symbol). This puts demands on what can be included
in the feature, the switching on and off has to be fast and the component has to come
back up fast. The idea was to turn off as many components as possible which where
fast enough to be turned off and able to come back up again, all with in the time of a
symbol. Different software and hardware solutions do to this needed to be found. With
this in mind components in the TX chain were studied once again.
In Table 4 the relevant components and their theoretical response times are presented.
The table covers the components which are physically possible to turn on and off in
such a short time period with out consideration of the consequences, such as stabilization times for PLLs.
Table 4: Candidates for TX micro sleep
Removed due to confidentiality.
The theoretical response times for the DAC and ADC are taken from their product
specifications and can be considered factual for optimal conditions [26][27]. The times
for the clocks are estimations of how long it takes for a gated clock to come back up
and judged to be a few clock cycles. No consideration to the resulting behavior of the
components losing the clock signal is taken. The PA driver and predriver are turned off
by closing the biasing and thereby very fast, consequences on the output signal is not
considered. The XYZ’s response time is dependent on how the pin used to power down
is programmed.
The next step was to figure out where and how the new components could be added in
the source code. The response times of the components also needed to be determined.
4.5.3
MIMO sleep
When the traffic is below a predetermined threshold the radio can be put in MIMO sleep
mode, this means that only one of the TX chains are used. Both RX chains remain operational since they are, as mentioned earlier, for all intents and purposes a single chain.
23
The threshold design enables longer response times since it allows for a preemptive start
up of the closed down chain.
The process of designing an improved MIMO sleep was similar to that of the cell sleep but
instead of making sure CPRI communication was maintained the retention of throughput was the parameter differentiating success from failure. The four UEs were connected
and setup as in the earlier tests. Measurements of the power consumption was collected
from the PSU.
24
5
Results
In order to be able to compare results to each other the power consumption for the radio
with no feature, the original feature and the new feature will be presented. The values
presented are with the testcard still in the radio, the testcard consumes 0.5W so the
actual consumption is 0.5W lower than the measured value. If nothing else is stated the
numbers are mean values over a 30 second period.
UVW and PQR are confidential components in the radio and their names have been
changed.
5.1
Current radio energy consumption
The radio’s power consumption depends on the traffic load and during testing it peaked
at 81W at maximum load. The consumption of the radio and PA in the traffic scenarios
is presented in Table 3 and shown in Figures 15 and 16 respectively.
PSU 36V
80
power, W
70
60
50
40
30 full
0
half
20
40
quarter
60
ten
80
100
idle
120
blocked
140
160
180
time, s
Figure 15: The PSU output power in the different scenarios.
In Table 5 the power consumption for the different scenarios with no features is listed
and also shown in Figure 16.
Table 5: The power consumption of the radio in the different scenarios.
Scenario
Full
Half
Quarter
Ten
Idle
Blocked cell
Power consumption W
73.43
67.45
60.52
56.12
53.15
31.85
To show the difference between the Idle and Quarter scenario, heat pictures were taken
while running. Figure 18 is in Idle and Figure 19 is in Quarter and shows increased heat
in the PA and TX low blocks.
25
PA 22-29V
50
45
40
power, W
35
30
25
20
15
10
5 full
half
quarter
ten
idle
blocked
0
0
20
40
60
80
100
120
140
160
180
time, s
Figure 16: The power consumed after the PA buck in the scenarios.
PA power
40
power, W
35
30
25
20
15
0
10
20
30
40
50
60
70
80
90
100
capacity, %
Figure 17: Power consumption plotted against load.
26
Figure 18: Heat picture of the radio in Idle mode.
Figure 19: Heat picture of the radio Quarter capacity mode.
27
5.1.1
Cell sleep
The components that were included in the final implementation and their power down
modes can be seen in Table 6.
Table 6: List of components and power down modes included in Cell sleep.
Confidential.
The clocks (clks) in Table 6 refers to all clocks on that specific branch. The power consumption in Cell sleep is listed in Table 7 together with the Ericsson implementation.
As the table shows the ”off state” of the radio was reduced by 42.7%.
Table 7: The power consumption for the different Cell sleep implementations.
Implementation
Ericsson
New
Power consumption W
31.85
18.23
Heat pictures were taken to highlight the differences between the two sleep modes.
Figure 20 is the Ericsson implementation and Figure 21 is the new Cell sleep implementation. The pictures show the heat signatures of the components cooling and a weaker
signature from the UVW and DC/DC block.
Figure 20: Ericsson Blocked cell implementation.
28
Figure 21: New Cell sleep implementation.
5.1.2
TX micro sleep
The first idea for the improvement of this feature was based on the theory that the
TX micro sleep feature that is implemented was a snippet of code. This would allow
for a few simple additions of the candidate components to that code since all interrupt
routines and such would already be handled. When studying this further it became
apparent that it was in fact a hardware implementation,. It required no lines of code,
only a few register writes for initial setup was necessary. The radio’s FPGA was used to
generate a strobe signal which was the propagated SIG1 signal. The signal is generated
from the data sent in the SF-info message sent by the DU. However further research
showed that there was hardware infrastructure to allow for a similar implementation of
the predriver and driver. In order to understand and to be able to study the behaviour
of the feature, measurement points were added to the SIG1, SIG2 and SIG3 signals.
The strobe signal for SIG1 was then studied with the oscilloscope and can be seen in
Figure 22.
In Figure 22 a single TTI for the strobed SIG1 signal is shown. The radio is currently
in idle mode and when the signal is high the radio is not transmitting and when the
signal is low it is transmitting. As the radio is in idle mode the pattern seen is the CRS
signaling pattern. The FPGA was setup to propagate to the driver as well. For the
predriver the signal was inverted since it is turned on when the signal is high and turned
off when it is low. In order to incorporate the other candidates presented in Table 4,
software would have to be written.
To be able to include the gating of the DAC clock, stabilization time of the PLLs for
the PQR LO and XYZ A needs to be determined. In a discussion with Kent Persson,
who works with designing the ASIC, he pointed out that the execution of software will
29
Strobe pattern
3.5
3
voltage, V
2.5
2
1.5
1
0.5
0
0
100
200
300
400
500
600
700
800
900
1000
time, µs
Figure 22: The strobed SIG1 signal.
be too slow to be included in TX micro sleep. The execution and transmission of the
SPI commands or GPIO toggling can not be guaranteed to finish in the specified time
intervals. Due to this all ideas of shutting off components controlled by GPIO or SPI
were abandoned.
The XYZ however is included in the TDD functionality and has a programmable pin
PIN1. The TDD block generates a strobe signal as well although it works with longer
time frames. The TDD switches at TTIs or milliseconds while the TX micro sleep
switches at symbols or microseconds. If the TDD strobe signal could be programmed to
switch at symbol level the XYZ could also included to the TX micro sleep. Unfortunately
the hardware in the TDD block does not have the capability to generate a strobe signal.
However, the two XYZs consume about 2.5W each, it would be beneficial to include
them in TX micro sleep. In order to test and demonstrate how beneficial this could be,
two solderings to the PIN1 pins were made allowing for a hardware workaround. This
was done by disconnecting the original PIN1 paths from the ASIC by removing the resistors R6A2 and R6A3, and instead connecting the SIG2 strobe signal to the PIN1 pin
to the XYZ, thus both were included in the TX micro sleep. In Table 8 the mean power
consumption for the different version are presented and in Figure 23 the measured data
is shown.
30
Table 8: The power consumption of the different implementations in Idle mode.
*Due to the first radio breaking this value is measured using another radio.
Implementation
Feature off
Original
Drivers
XYZs
Power consumption W
53.15
44.43
41.63*
39.44
TX micro sleep
mean :44.43W
mean :39.44W
60
power, W
55
50
45
40
35
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
time, ms
Figure 23: TX micro sleep in idle with mean values for original and new implementations.
The implementation ”Drivers” is the original implementation with the addition of the
drivers and predrivers. The implementation ”XYZs” is the ”Drivers” implementation
with the addition of both the XYZs. This results in the final implementation of TX
micro sleep.
To visualize the difference between the implementations heat pictures were taken. Figure 24 is the original implementation to be contrasted with Figure 25 which is the new
implementation. The radio is in Idle mode when the pictures are taken and had reached
a stable temperature.
A test using the scenarios in Table 3 was also done and the throughput and power
consumption was logged. The power consumption is presented in Figure 26 and the
throughputs were as expected, in other words exactly 50%, 25% and 10% of the radio’s
maximum capacity. In Table 9 the values are presented with corresponding savings in
%, note that the values in ”No feature” are the same as in Table 5.
Table 9: PSU power in W with no features compared to the improved TX micro sleep.
Implementation
No feature
New
% saved
Half
67.5
66.2
1.9
31
Quarter
60.6
55.7
8.1
Ten
56.1
48.8
13.0
Idle
53.1
38.7
27.2
Figure 24: Ericsson TX micro sleep implementation.
Figure 25: New TX micro sleep implementation.
32
PSU power
70
Original
New
65
power, W
60
55
50
45
40
35
0
5
10
15
20
25
30
35
40
45
50
capacity, %
Figure 26: Original and new PSU power at different capacities.
5.1.3
MIMO sleep
The components that were included in the final implementation is presented in Table
10.
Table 10: Components that are turned off in MIMO sleep.
Confidential.
Table 11 shows the mean power consumption of the original implementation and the
improved one. These values are the mean calculated from data which of some can be
seen in Figure 27.
Table 11: The power consumption of the MIMO sleep implementations.
Implementation
Ericsson
New
Power consumption, W
42.38
39.43
The radio was in Idle mode. Figure 28 shows the heat signature of the original implementation, Figure 29 shows the new version.
33
MIMO sleep
47
mean :42.38W
mean :39.43W
46
45
power, W
44
43
42
41
40
39
38
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
time, ms
Figure 27: MIMO sleep data.
Figure 28: Original MIMO sleep implementation.
34
Figure 29: New MIMO sleep implementation.
5.1.4
Feature combination
The biggest improvement is achieved when combining TX micro sleep and MIMO sleep.
The effects of TX micro sleep is reduced since there only being one active branch when
MIMO sleep is activated. However the consequences of closing down one branch lets
the combination come down to consumption levels close to that of the Ericsson implementation Blocked cell while still being operational. Table 12 presents the original
implementations combined, the new and the Ericsson Blocked cell. The measurement
data for the original and the new implementations is shown in Figure 30.
Table 12: The power consumption of the different feature implementations combined
and the Ericsson Blocked Cell for comparison.
Implementation
Ericsson
New
Blocked cell
Power consumption W
38.08
32.61
31.85
This once again highlighted with heat pictures, Figure 31 is the combination of the
original implementations, Figure 32 is the combination of the new.
35
TX micro sleep and MIMO sleep
46
mean :38.08W
mean :32.61W
44
power, W
42
40
38
36
34
32
30
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
time, ms
Figure 30: TX micro sleep and MIMO sleep with mean values for the original and the
new implementations.
Figure 31: Combination of Ericssons implementation of TX micro sleep and MIMO
Sleep
36
Figure 32: Combination of the new implementations
5.2
Buck dimensions
The PSU supplies both the PA and TRX buck converters and measurements are done
at the output of the converters, see Figure 13, due to this the power of these two buck
converters are added together when calculating the efficiency. The PA and TRX buck
converters’ power and efficiency can be seen in Table 13. The total is calculated by
adding PA and TRX together and the efficiency by dividing this total by the PSU
measured power.
Table 13: PA and TRX buck power in W and the efficiencies in % at different modes.
Confidential.
The power going through the TRX buck is more or less consistent during different modes
until the radio is set in blocked cell. This can be read out from Table 13 and seen in
Figure 33. The data for full, half, quarter and ten will not be presented for the remaining buck converters as they show the same values in these modes as in Idle. In Table
14 the combined efficiency is calculated for the remaining buck converters. The power
going through the buck converters were added to create the total which is divided by
the power passing through the TRX buck converter. An important note is that the
power passing through the switch is subtracted from the TRX and not added to the
other buck converters when calculating the efficiency since it is not a converter. The
mean values in Table 14 are calculated from the data shown in Figures 34, 35, 36 and 37.
The potentiometers that adjust the voltage for the two adjustable buck converters were
measured and their settling and rise time can be seen in Figures 38 and 39. The value
37
Figure 33: Confidential.
Table 14: Buck power and efficiencies at different modes.
Confidential.
(a) Confidential.
(b) Confidential.
Figure 34: Confidential.
(a) Confidential.
(b) Confidential.
Figure 35: Confidential.
(a) Confidential.
(b) Confidential.
Figure 36: Confidential.
(a) Confidential.
(b) Confidential.
Figure 37: Confidential.
written to the potentiometers was 0 to 255 and 255 to 0, i.e. the maximum possible
range.
38
VCC settle/rise time for voltage
voltage, V
0.95
0.9
0.85
0.8
0.75
0
0.5
1
1.5
2
2.5
3
3.5
4
2.5
3
3.5
4
time, ms
voltage, V
0.9
0.85
0.8
0.75
0
0.5
1
1.5
2
time, ms
Figure 38: Rise and settling time for the potentiometer.
PA settle/rise time for voltage
voltage, V
30
25
20
15
0
2
4
6
8
10
12
14
16
18
20
12
14
16
18
20
time, ms
voltage, V
35
30
25
20
15
0
2
4
6
8
10
time, ms
Figure 39: Rise and settling time for the potentiometer.
39
6
Discussion and conclusion
In the conducted study limits were pushed and some possible issues neglected. This
approach was necessary in order to be able to find new possibilities and change things
that always have been in a certain way. During the process we encountered setbacks
ripping ideas apart however by adapting these ideas some could still be implemented.
The ideas that were not possible to implement are discussed and noted, and hopefully
future hardware and software designers will take them into account when designing next
generation radios.
We have not taken RF signal quality and wear and tear of components into account
in the study. When checking whether or not a feature worked we tested if we still could
communicate with the radio and if we had the desired throughput. Basically we created
proof of concepts and were satisfied if the radio functioned while running the feature.
The trial and error method that was used might have come with some unwanted and
undocumented consequences. When using the ”I wonder what this does?” approach and
the only parameter for evaluation is the power consumption you might end up with a
radio in a quite undefinable state. Some registers might not be reset at a reboot and
therefore contain values they are not expected to contain. When writing to registers
and sending SPI commands the wrong address or values might have been used giving an
unexpected and possibly undocumented results. The original radio finally gave up on us
and we decided to modify a new radio to allow for further demonstrations. We are not
sure why the radio stopped working but one thought is that it could be the solderings
damaged the PCB. The damaged did not occur straight away but over time because
the radio would act normally and then during operation it would restart or not give
maximum throughput. The new radio differed in power consumption in the different
tests run compared the first radio. In general it would consume slightly less, the reason
for this is unknown.
6.1
Buck dimensions
During operation the DC/DC buck converters are very efficient with efficiencies ranging
from 93-95%. At first we thought that these values were incorrect because we expected
that the buck converters were dimesioned for the larger Macro radio. The results however came out the same after multiple measurements. The resistors have a 1% margin
of error so if all the buck converters in step three (see Figure 13) would have been 1%
below the specified value the efficiency would only have changed 1-2%. This scenario is
very unlikely so instead we need to look at the buck converter’s properties. In Figure
40 an efficiency plot for the 1.8V buck converter is shown. The efficiency is higher if the
difference between input and output voltage is smaller and is almost consistent between
1 and 3 A, looking at Vin = 5V. It is only when the current is less than 0.5-0.6A that
the efficiency decreases below 90%.
In Table 14 the power per power domain is listed. In order to follow the efficiency curve
the power is converted to current, as seen in Table 15. An important note is that Figure
40 looks different for all the other buck converters. As the power decreases from e.g. 3A
to 2A the efficiency will increase, so only once the current is below a certain level the
efficiency will quickly decrease. This concludes that there is definitely a possibility that
these high efficiencies are correct.
We had ideas to adjust the two adjustable buck converters voltages however as seen in
40
Figure 40: Efficiency plot for the 1.8V buck converter [19].
Table 15: Current through the buck converters in sleep mode.
Confidential.
Figures 38 and 39 it takes very long time for the voltage to reach the desired value. The
application areas for these adjustments are therefore limited.
6.2
Cell sleep
In Table 14 the power in Cell sleep is 14.7W for step 3, in Table 13 15.47W for step 2 and
18.24W for step 1. The steps can be seen in Figure 13. The losses in step 1 to 2 and 2
to 3 alone are around 20% or 85% and 95% respectively. The buck converter’s efficiency
depends on the current, which decreases as more components are turned off, motivating
a low-current buck converter as the radio enters cell sleep. So a solution to this would
be to have two 5.1V converters, one which operates at normal use (high currents) and
one at cell sleep (low currents). This would increase the DC/DC unit efficiency in cell
sleep and the radio would consume less energy. For example the efficiency of the TRX
buck converter would be improved by 5% (from 85% to 90%) in Cell sleep, the overall
efficiency would go from 80.8% to 85.5% and we would save an additional 1W, dropping
down to 17.2W from 18.24W.
The optimal power save feature for cell sleep would be a ”wake on CPRI” function,
i.e. the radio is entirely shut off with the exception of the SFP which maintains connection with the DU. The SFP should be able to boot the radio when told to do so,
this would require quite large changes in the hardware and software. The radios today
are designed assuming the unit is constantly turned on generating heat and keeping
moisture out, so condensation is an issue that will have to be addressed in new a design.
By having a separate DC/DC branch only powering the SFPs and utilizing the already
existent DC/DC supervision circuit the feature could easily be implemented. When the
radio is needed a signal would be sent through the CPRI communication, the SFP would
41
respond by sending a signal to the DC/DC supervisor which powers up the remaining
DC/DC units, booting up the radio as normal.
6.3
TX micro sleep
After we had completed cell sleep we had acquired enough knowledge to create a power
save mode in which the radio runs and functions. After hearing about TX micro sleep
we started looking into which components that could be shut down in the small window
of a symbol. We understood there were quite many possibilities as most components
have very short response times. However when we started digging deeper we realized
that there were some limitations that would difficult to overcome.
A lot of time was spent trying to measure the lock time for PLLs and in the end
we did not find any satisfying method to do so. The clock signal going into the clock
buffer from the PQR and the output LO signal from the XYZ (this clock locks to the
signal from the clock buffer) were measured with an oscilloscope. By switching off the
PQR clock and switching it back on we could see the stabilization time of the PQR clock
and how the XYZ’s LO phase and frequency adapted. After approximately 10-20 clock
cycles (approximately 60 ns) the signals seemed to be in phase and frequency, however
this cannot count for a precise or very scientific method. We attempted to use vector
and frequency analyzers instead of the oscilloscope, however without any success.
We did not spend any time in optimizing the delay and offset for the SIG3 or SIG2
signal. When optimizing these the XYZs configuration together with the SIG2 signal
both have to be taken into account as they share the same signal. An optimization of
these might give even more savings since there might be more time to take advantage
of it would also ensure proper functioning.
The strobed signal SIG1 during one TTI is shown in Figure 22. It has an delay, i.e.
it turns on and off a bit later which must mean that the signal passes later here than
through the drivers. This makes sense because the signal controls the last amplification
in the amplifying chain. The maximum time it is possible for the PA and drivers to
be turned off is 10/14 = 71.43%, as at least four symbols are used to send CRS in idle
mode. The sampling rate is 2.5MHz (2500 data points for one TTI) and to calculate
the time the PA is off all the measurement points above a 0.5V threshold are added
together. The result is 1784/2500 = 71.36% which more or less is exactly the maximum
concluding that the rise time for the PA is instantaneous.
Kent Persson told us in a telephone conversation that in the next generation of the
ASIC called ASIC2 there will be more strobing options and SPI commands will also be
possible to strobe. This means that on that platform TX micro sleep can be even more
effective. It will be possible to include clock gateing and other components to the feature.
In Figure 23, showing the radio’s power consumption, the maximum output is the same
for Ericsson’s and our implementation, only the base power is lower. The reason is
because all the components (SIG1, SIG2, SIG3 and XYZ) are up and running when
transmitting and turned off when not.
42
6.4
MIMO sleep
When transmitting from two antennas different measures of creating diversity is possible
which can improve the signal quality at the receiver by supplying two diversified signals
sending the same information. The receiver then combines the two signals with advanced signal processing to create one signal with better quality. Two antennas can also
be used to create two parallel channels sending different information on two channels
on the same frequency. This is called spatial multiplexing and allows for better use of
bandwidth, i.e. increases throughput. When the signal strength is good this is what the
two antennas will be used. When the signal strength becomes very bad beam-forming
should be used instead to improve the signal. However this is not used, the modulation
is degraded instead. So when turning off one branch the maximum throughput of the
radio is lowered, but also better matched with the demanded throughput. Switching off
on RX branch in addition will further reduce the power consumption. This will however
affect the uplink signal quality since the benefits of spatial diversity are lost. It is hard
to predict the behavior of UEs and to determine that the signal strength is good enough
with only one antenna might be difficult. To switch off only the components that come
back up fast, for example the LNAs, might be a possible solution since it allows for fast
on and off switching.
To be able to scale the available capacity with the traffic load makes sense because
there is no need to have the whole radio up and running when only half supplies the
demanded capacity. In an area where there are periods of time of which the radio does
not run at full capacity, this feature will reduce the power consumption dramatically.
However there are some further improvements that can be done to the feature. Currently it is not possible to gate the clocks for DL B in the ASIC without it failing, gating
these clocks would give additional savings of around one watt.
The data for MIMO sleep is plotted in Figure 27. The pattern is identical, however
the overall power consumption has been reduced. This is due to that components not
used in branch B are permanently turned off.
6.5
Combined features
The greatest reduction of power consumption is achieved when the TX micro sleep feature is combined with the MIMO sleep feature. This reduces the power consumption
dramatically and takes it down to around 32W in Idle mode which is very close to what
the radio consumes in Blocked Cell mode. In other words, we managed to reduce the
power consumption of the radio while still in operation to a level close to the current
Ericsson implementation used to turn the radio off. We can now have the radio functioning normally however with reduced throughput. It consumes as little power as if
it was turned off in regards of what is possible today. The power consumption will of
course still increase with the load put on the radio and at full capacity the features will
have no effect and no savings will be possible.
This combined feature could be implemented on a large number of sites. In the beginning of the report Figure 4 shows how much traffic passes through sites and as we
can see half of them are low traffic sites. The combined feature would have a great
impact on these sites since it scales with the demanded load. If there is low traffic
there are many symbols where the radio does not transmit and this means that the
feature has more active time. The capacity demand on the medium sites might be more
than what one antenna could provide however during some time periods the combined
feature would be applicable. TX micro sleep will still be active and reduce the power
43
consumption. At the high traffic sites the power saving features will not have much
impact as the radio is sending continuously. Only 10% of the sites are high traffic sites
so the remaining 90% could all reduce their power consumption significantly.
6.6
Scalability
During the study of the radio it became apparent that all components are always up
and running, allowing for full capacity at any time, even though only a small percentage
of the radio’s capacity is needed. The subject has been discussed earlier, to scale the
available capacity of the radio to the demanded is clearly beneficial leading to a reduced
power consumption. The DU always knows exactly how much capacity is needed and
when, making a scalable system possible. One way to do this is the MIMO sleep feature,
we now have a system with two ”gears”, full and half capacity. We want to introduce
more gears, we want a system that continuously changes gears depending on the demand
of capacity.
One easy way to introduce gears would be to change the clock frequency for the radio, when the traffic is low the clock frequency, or speed, of the system should be low.
As the demand for capacity increases the radio switches gears; it increases the clock
frequency. If the frequency is lowered the voltage can be reduced, leading to additional
savings. We researched the possibilities to reduce the frequency of the radio and were
told ”It is not possible to reduce the frequency.”, we were not deterred by this and kept
trying. However the task proved to cumbersome and was abandoned due to lack of time,
however still convinced that it is possible. The radio itself can easily be clocked down
but when it runs on a different clock than the DU problems arise. This could however
be dealt with by increasing the clock speed in the components where those problems
occur. These components have to be identified and the clock frequency determined.
The gears should also include components of the radio. The MIMO sleep feature for example include components that take about 500µs to turn on making it unfit for switching
on and off fast. By not dividing components into features and instead categorize them
by their function and response time and asking the question ”What needs to be turned
on?”, a truly scalable system can be designed. This will be addressed more under 6.8.
6.7
Hardware
Many components come with the different power modes and some of these components
have the pin to ground not allowing control and others can be activated by SPI or GPIO.
To fully utilize the power saving capabilities of the components, they should not be hardwired to ground and we need to be able to access them instantly. Hardware needs to
be modified to enable fast communication with the components whether it is by GPIO
or SPI. Rapid interaction with the components enable them to be turned on and off
faster and therefore be utilized in shorter time windows. The ability to generate strobes
for all components on the board would be incredibly useful for many implementations
since it is known beforehand when the radio needs to transmit. Components should also
be able to be controlled individually. In the current implementation many of the RX
components are controlled pairwise which makes scaling the RX chain impossible.
In general the components should be optimized out of a energy perspective with different power save modes. The XYZ has programmable pins which execute when the pin is
set high, this allows for custom sleep modes to be constructed. This is useful when the
internal components have different response times and the preprogrammed sleep modes
44
are too slow to be utilized in short time frames. It is also desirable to have components
which have features that can be activated easily, by toggling a pin for example.
Looking at older radios, the RRUS 12 for example, many components cannot be controlled at all. The RRUS 12 has the same XYZ as the Micro but lacks the option to
control it by the pins PIN1 and PIN2 which we have used. The next generation radio
is supposed to have more and faster controlability.
6.8
Making the radio intelligent
With all components categorized by their function and response time the question ”What
needs to be turned on?” can be answered by an intelligent system. The idea is to create
a smart system, a type of artificial intelligence, that makes predictions based on historical data and current readings and then answers the question by turning everything
else off. It will not scale by activation or deactivation of whole features but individual
components, and maybe not turn an component off entirely but put it in a sleep mode,
depending on the current and predicted future demand. This allows for only the absolute necessary components to be active on any given time.
It seems preferable to put this intelligence in DU since it knows the current number of
UEs connected to which cell, it controls handovers and contains computational power.
45
7
Further work
Confidential.
8
References
References
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Miljö och energidepartementet. Mål för energi. 2015. url: http://www.regeringen.
se/regeringens-politik/energi/mal-och-visioner-for-energi/.
[2]
Tele2. Environmental Responsibility. 2016. url: http://om.tele2.se/miljooch-hallbarhet/.
[3]
Telia. Miljö och hållbarhet. 2015. url: http : / / www . teliacompany . com / en /
sustainability/responsible-business/environmental-responsibility/.
[4]
Vodafone Germany. Energiesparmaßnahmen. 2016. url: http://www.vodafone.
de/unternehmen/klimaschutz/energiesparmassnahmen.html.
[5]
Deutsche Telekom. Mission: 20 percent fewer CO2 emissions. 2016. url: http:
//www.telekom.com/corporate-responsibility/climate-and-environment/
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[6]
Vodafone Italy. Efficienza Energetica. 2016. url: http : / / www . vodafone . it /
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TIM. TIM SUPPORTS #GLOBALGOALS. 2016. url: http : / / in . tim . it /
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backgrounders/global_services_press_backgrounder.pdf.
[11]
Sköld Dahlman Parkvall. 4G LTE/LTE-Advaced for Mobile Broadband. Academic
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[12]
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[13]
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[14]
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Texas Instruments Edgar Pineda. Clocks Basics in 10 Minutes or Less. 2010. url:
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46
[20]
Robert W. Erickson Dragan Maksimovic. Fundamentals of Power Electronics.
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[26]
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[27]
Confidential. -. -. -. -.
47
9
9.1
Appendix
Abbreviations
3GPP
ADC
ASIC
BE
CPRI
CRS
DAC
DPA
DPD
DSA
DU
FDD
FE
FPGA
GPIO
LDO
LESS
LNA
LO
LTE
LTU
LVDS
LVPECL
MIMO
MPA
PA
PCB
PLL
QAM
RAN
RX
SERDES
SFP
SPI
TDD
TRX
TTI
TX
UE
VCO
3rd Generation Partnership Project
Analog to Digital Converter
Application Specific Integrated Circuit
Back End
Common Protocol Radio Interface
Cell Specific Reference Signaling
Digital to Analog Converter
Driver PA
Digital Pre Distortion
Digital Step Attenuator
Digital Unit
Frequency-Domain Duplex
Front End
Field Programmable Gate Array
General Purpose Input Output
Low Drop Out regulator
Low Energy Scheduler Solution
Low Noise Amplifier
Local Oscillator
Long Time Evolution
Local Timing Unit
Low Voltage Differential Signal
Low Voltage Positive Emitter-Coupled Logic
Multiple Output Multiple Input
Main PA
Power Amplifier
Printble Circuit Board
Phase Locked Loop
Quadrature Amplitude Modulation
Radio Access Network
Receiver
Serializer/Deserializer
Small Form-factor Pluggable
Serial Peripheral Interface
Time-Domain Duplex
Transceiver
Transmission Time Interval
Transmitter
User Equipment
Voltage Controlled Oscillator
Table 16: Commonly used abbreviations.
48