Chapter 3 Answers

Answers to Exercises

1. a. In general, Sigfox is a very low data rate network which uses a very small spectrum. LoRaWAN supports both 250 kHz and 125 kHz bandwidth. Depending on spreading factor and channel bandwidth, the LoRa data rate is between 300 bps and 50 kbps. Sigfox uses ultra narrow spectrum of 100 Hz, the amount of uplink as well as downlink data rate is very low. The maximum data rate of Sigfox is around 100 bps. Choice c is not correct. It is correct that the LoRa uses six spreading factors where higher spreading factor provide longer range and lower data rate, and lower spreading factors provide higher data rate at the expense of lower range. However, still with the highest spreading factor, the maximum data rate of LoRa is higher.
2. b. NB-IoT and Sigfox do not support mobility. LTE-M supports mobility even with high speed vehicles. The LoRaWAN supports mobility, but LTE-M has better features.
3. c. LTE-M, NB-IoT, and Sigfox are cellular. LoRaWAN is not based on cellular network.
4. b. They are not the same. LoRa defines the physical layer (L1) of the system, LoRaWAN defines the protocols over the LoRa and it is the network architecture which operates in a non-licensed band. LoRa is developed by Semtech and LoRaWAN by LoRa Alliance.
5. b. Operators have deployed LTE-M network using 1.4, 3, 5, 10, 15, or 20 MHz spectrum. There are some early deployments that are based on 1.4 MHz spectrum. LTE-M uses 1.4 in Release 13 and 5 MHz in Release 14 and above. Therefore, if an operator uses 1.4 MHz spectrum for LTE, LTE-M Release 14 cannot be deployed in that center.
6. c. LTE-M signaling is very similar to legacy LTE. In LTE-M, there have been more changes to PDCCH control channel compared to the other channels. The new channel is called MPDCCH which stands for MTC physical downlink control channel. MPDCCH is a special type of PDCCH designed for IoT operation. Most channels in LTE-M are very similar to legacy LTE, except that the repetition and frequency hopping have been added to channels.
7. d. They are mostly different, but there are a few similarities. NB-IoT has made substantial changes to the LTE signaling and has introduced many new channels in contrary to LTE-M that was very similar to legacy LTE.
8. c. The duplexing is FDD, but the device should alternate between transmission and reception.
9. a. Each radio frame in LTE is 10ms, and is divided to 10 sub-frames. Each sub-frame has two slots each 0.5ms.
10. a. Access permission of a UE to the network for initiating data transfer. When a UE wants to transfer data, it should start a process called random access. To do that, the UE should send a preamble in Physical Random Access Channel (PRACH).
11. b. It is one to several milliseconds. The values of  T_D, T_DUS, T_UDS for LTE-M are 1ms, 3ms, 3ms, respectively.
12. a. the correct answer is in-band mode. In this mode of deployment, one PRB in LTE spectrum is dedicated for NB-IoT in both the DL and UL. The rest of LTE spectrum is dedicated to non-IoT data transfer.
13. c. By introduction of repetitions. NB-IoT neither increases the power transfer, nor changes the frame structure. It uses repetitions to gain 20 dB to reach to the locations with poor radio condition.

Answers to Review Questions

1. The Third Generation Partnership Project (3GPP) is the global technical body which develops technical specifications for mobile communication system. It is not for standardization. 3GPP writes technical specifications, to be transferred into standards by the organizational partners. Therefore, the 3GPP partners are responsible for standard based on technical specifications produced by 3GPP. Overall, we can say that the 3GPP and its partners have made standards for 2G, 3G, 4G and 5G cellular networks.
2. For example, 4G was first introduced in Release-8 and is continued to evolve in higher releases.
3. Global availability of GSM in lower frequency bands of either 850 or 900 MHz band has enabled GSM to provide a good coverage. GSM using a simpler technology as compared to more advanced generations of cellular network. This means that the price of GSM mobile devices would be cheaper as compared to 3G, 4G and 5G technologies. This also makes GSM an attractive choice for IoT technology.
4. LTE-M has higher data rate, uses larger spectrum, and provides mobility. NB-IoT has lower data rate, uses smaller spectrum, and does not support mobility.