NARDA SRM-3006 Manual 

Subject to change 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 Authors: Mark Reinhard, Helmut Keller Sandwiesenstr. 7 72793 Pfullingen, Germany Tel.: +49 7121 9732-0 Fax: +49 7121 9732-790 E-mail: [email protected] www.narda-sts.com Figure 1: Narda SRM-3006

Subject to change 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)

Subject to change 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

Subject to change 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

Subject to change 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

Subject to change Narda Safety Test Solutions GmbH Sandwiesenstrasse 7 72793 Pfullingen, Germany Phone: +49 (0) 7121-97 32-0 Fax: +49 (0) 7121-97 32-790 E-mail: [email protected] www.narda-sts.com Narda Safety Test Solutions 435 Moreland Road Hauppauge, NY 11788, USA Phone: +1 631 231-1700 Fax: +1 631 231-1711 E-Mail: [email protected] www.narda-sts.us Narda Safety Test Solutions Srl Via Leonardo da Vinci, 21/23 20090 Segrate (Milano) - Italy Phone: +39 02 269987 1 Fax: +39 02 269987 00 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