NARDA SRM-3006 User manual

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Safety Radiation Meter
SRM-3006
Application Note 1106
Code-selective measurements with the SRM-3006
Using the LTE-TDD option
With firmware release 1.5.0, the SRM 3006 can also demodulate TDD mode LTE
signals. This article provides an overview and describes the main differences with
FDD mode.
Contents
1 The LTE E-UTRA frequency bands ......................................... Page 2
2 The LTE duplex modes ........................................................... Page 3
3 LTE-TDD uplink and downlink configurations .......................... Page 4
4 Using the SRM-3006 LTE-TDD option ..................................... Page 5
5 Further literature ...................................................................... Page 6
© August 2017
Narda Safety Test Solutions GmbH
A
uthors:
Mark Reinhard, Helmut Keller
Sandwiesenstr. 7
72793 Pfullingen, Germany
Tel.: [phone]
Fax: [phone]
E-mail: [email protected]
www.narda-sts.com
Figure 1: Narda SRM-3006

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1 The LTE E-UTRA frequency bands
LTE stands for Long Term Evolution. This is the fourth generation of mobile telecommunications networks, called 4G
for short. The specification process for LTE began in around 2004, and it took another five years or so until the first
LTE networks came on line between 2008 and 2010. LTE is now operational almost everywhere in the world, and has
already developed further to LTE Advanced, or 4.5G. It is likely that LTE will also play an important part in the coming
decades, particularly in connection with the fifth generation mobile telecommunications standard (5G).
The LTE frequencies are based on the E-UTRA specification, which stipulates frequency bands between 700 MHz
and 3700 MHz. (E-UTRA band 46 is actually at 5200 MHz, but is not used according to information available when
this article was written.) Some E-UTRA bands are listed in Table 1 along with their frequency and duplex information.
E-UTRA band Frequency band
[MHz] Frequency range [MHz] Duplex mode
1 2100 UL: 1920 – 1980 DL: 2110 – 2170 FDD
3 1800 UL: 1850 – 1910 DL: 1930 – 1990 FDD
7 2600 UL: 2500 – 2570 DL: 2620 – 2690 FDD
12 700 UL: 699 – 716 DL: 729 – 746 FDD
30 2300 UL: 2305 – 2315 DL: 2350 – 2360 FDD
33 2100 1900 – 1920 TDD
38 2600 2570 – 2620 TDD
40 2300 2300 – 2400 TDD
42 3500 3400 – 3600 TDD
44 700 703 – 803 TDD
65 2100 UL: 1920 – 2010 DL: 2110 – 2200 FDD
Table 1 makes it clear that some frequency bands definitely overlap. This basically means an increase in spectrum
management, particularly in frontier regions, and there is a risk of interference. For example, bands 12 and 44 have
spectral components in common, as do bands 30 and 40. Table 1 also shows that each LTE frequency band is
allotted one of two specific duplex modes: either frequency division duplex (FDD) or time division duplex (TDD). (A
look at all the E-UTRA bands shows that bands 1 through 32 and 65 through 71 only allow FDD, while bands 33
through 46 only allow TDD.) The duplex mode describes the dimension in which the uplink and downlink are
separated from each other. This is described in detail below.
At the time this article was published, the majority of LTE networks worldwide used FDD mode. According to the
Global Mobile Suppliers Association (GSA) there were 95 LTE TDD networks in 54 countries worldwide in operation
at the end of January 2017. At that time, there were 32 network providers operating both LTE FDD and TDD
networks. TDD networks are frequently found in China and India, but also in Canada, the USA, and some African
countries, particularly Ghana and Nigeria. LTE in Europe mainly uses FDD mode, but TDD networks do exist in
Belgium, Finland, Ireland, Italy, The Netherlands, Sweden, Slovakia, Spain, and Russia.
Table 1: E
-
UTRA / LTE frequency bands (UL: uplink, DL: downlink) and duplex modes (as of April 2017)

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2 The LTE duplex modes
The duplex mode in cellular mobile telecommunications systems such as 2G, 3G and 4G refers to the way
communication between the handset and the base station takes place, that is, how the uplink and downlink are
separated from each other. In 2G as well as in 3G and most of the 4G frequency bands (see Table 1) a specific
frequency range is reserved for the uplink (i.e. the wireless signal from the handset to the base station). At the same
time, a different exclusive frequency range is used for the downlink (from base station to handset). The two
communications channels are thus separated by their frequencies, and this is therefore called frequency division
duplex mode.
LTE stipulates TDD bands as well as FDD bands. TDD means that the two communications channels are separated
from each other in time rather than in frequency. The uplink and downlink operate on the same frequency, but
alternate with each other in a strictly controlled manner. This is illustrated in Figure 1.
The diagram of FDD on the left of Figure 1 makes it clear that the uplink and downlink operate on two different
frequencies or bands, but can operate simultaneously. It is important to remember that this simultaneous operation is
not random, but follows a specific protocol depending on the mobile communications standard being used. It should
also be noted that some of the available timeslots can be empty, depending on the volume of data traffic (blank boxes
in the diagram).
TDD is shown on the right in Figure 1. This clearly shows that only one frequency band is used, and the uplink and
downlink signals must alternate with each other as a consequence. The uplink and downlink must never be allocated
the same resources (i.e. number of timeslots). On the contrary, the downlink is typically given more resources, as the
handset will generally download more data than it uploads. This is indicated by the larger number of blue DL boxes in
Downlink (DL)
Uplink (UL)
Figure 2: The difference between FDD (left) and TDD (right)
Time
Frequency
Frequency
Division Duplex Time
Division Duplex

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Figure 2. A protocol is also required for this, to ensure that the uplink and downlink in TDD alternate without conflicts.
Such a protocol is likely to be quite complex for a modern communication technology like LTE. It can be illustrated
simply as being like a conversation between two persons using a simple walkie-talkie link operating on one
frequency. When one person is talking, the other is listening, and vice versa. The two persons take turns to talk. If
they both try to talk at the same time, a conflict occurs and communication becomes unintelligible. If the first person
has more to say than the second, they would require more resources, just like the TDD downlink in Figure 1.
3 LTE-TDD uplink and downlink configurations
As explained in section 2, LTE-TDD is subject to a specific protocol. Among other things, this determines the
resources / number of timeslots that are to be allocated to the uplink and downlink within a given time period. This is
referred to as the uplink / downlink configuration of a TDD network. Seven configurations, numbered 0 to 6, are
defined for LTE-TDD, as shown in Figure 3. These allocate more resources to either the downlink or the uplink, as
appropriate.
Uplink / downlink-
configuration
Sub frame number
0 1 2 3 4 5 6 7 8 9
0 DL SSF UL UL UL DL SSF UL UL UL
1 DL SSF UL UL DL DL SSF UL UL DL
2 DL SSF UL DL DL DL SSF UL DL DL
3 DL SSF UL UL UL DL DL DL DL DL
4 DL SSF UL UL DL DL DL DL DL DL
5 DL SSF UL DL DL DL DL DL DL DL
6 DL SSF UL UL UL DL SSF UL UL DL
However, as Figure 2 focuses on the LTE standard, the term used is sub frames rather than resources or timeslots. A
sub frame has a duration of one millisecond according to the specification. Ten sub frames make up a so-called radio
frame, which is the largest unit in the LTE frame structure. A sub frame can be used for either the downlink (DL) or
the uplink (UL), as shown in Figure 2. A sub frame can also function as a special sub frame (SSF). The special sub
frame has various functions: It contains pilot signals for the uplink and the downlink, and a large part of the special
sub frame is allocated as so-called guard time. As with many other communications systems, no signals are
transmitted during the guard time. This serves to provide immunity to the negative effects caused by multipath
propagation.
Figure 3: LTE-TDD uplink and downlink configurations

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4 Using the SRM 3006 LTE-TDD option
It is now also possible to demodulate LTE TDD signals on the SRM 3006 with firmware release 1.5.0. Sections 1 to 3
above have described how LTE TDD functions differently to LTE FDD and how it therefore needs different treatment
in the SRM. The main distinction between the FDD option and the TDD option is that the particular uplink / downlink
configuration can be set additionally in the TDD option.
If the uplink / downlink configuration being used in an LTE TDD network is definitely known, this can be set
appropriately during a measurement with the SRM 3006, as illustrated in Figure 3. The SRM benefits from a slightly
reduced measurement uncertainty if the correct configuration is set. If a setting is chosen that does not correspond to
the actual uplink / downlink configuration, the risk of over- or under evaluation increases significantly. The
configuration setting “0 (Recommended)” is an exception to this. This setting can be used universally for all network
configurations. When set to “0”, the SRM focuses on sub frames 0 and 5 and also on the reliable downlink
components in the special sub frames (i.e. sub frames 1 and 6). These four sub frames always carry downlink
signals, regardless of the uplink / downlink configuration, as is shown clearly in Figure 3 and by the explanation of
SSF given above. The configuration setting “0 (Recommended)” should therefore be used as the standard setting,
and should also be used if the actual uplink / downlink configuration is not definitely known.
Remember that the SRM can also demodulate TDD signals when the setting “0 (Recommended)” is chosen, even
when this does not correspond to the actual configuration of the network. If the actual configuration is set, this will
merely achieve a slight improvement in the measurement uncertainty. If a configuration other than “0
(Recommended)” is set and this does not correspond to the actual configuration of the network, then the
measurement uncertainty will be significantly degraded and even the basic demodulation function will no longer be
assured!
Figure 4: LTE TDD option in the SRM 3006 with uplink / downlink configuration selection

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Narda Safety Test Solutions GmbH
Sandwiesenstrasse 7
72793 Pfullingen, Germany
Phone: [phone]
Fax: [phone]
E-mail: [email protected]
www.narda-sts.com
Narda Safety Test Solutions
435 Moreland Road
Hauppauge, NY 11788, USA
Phone: [phone]
Fax: [phone]
E-Mail: [email protected]
www.narda-sts.us
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E-Mail: [email protected]
www.narda-sts.it
® Names and logo are registered trademarks of Narda Safety Test Solutions GmbH and L3 Communications Holdings, Inc. – Trade names are the trademarks of their respective owners.
5 Further literature
This article describes the LTE-TDD option in the SRM 3006. Further information about LTE as well as UMTS can be
found on the Internet at: www.narda-sts.com/de/selektiv-emf/srm-3006
As well as chapter 12.6 “LTE-TDD” in the SRM 3006 operating manual, the following three documents available from
the Narda STS website are of particular interest:
- Immission measurements in the vicinity of LTE base stations (Part 1: Fundamentals)
Application Note AN 1062
- Immission measurements in the vicinity of LTE base stations (Part 2: Measurement methods)
Application Note AN 1064
- Using UMTS mode
Technical Note 10