LUNDS TEKNISKA HÖGSKOLA

Inst. för telekommunikationssystem

Tentamen i AVANCERAD TELEKOMMUNIKATION, 2010-08-26

Time: 14.00 – 19.00

Number your pages! Write your name on each of the pages!

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Questions from the book:Your answers to the five questions from the book should be written on just one double page sheet!

1) (2.8): What are the main problems of signal propagation? Why do radio waves not always follow a straight line? Why is reflection both useful and harmful?

2)(3.6): Consider duplex channels, what are alternatives for implementation in wireless networks? What about typical wired networks?

3)(4.5): Name the main elements of the GSM system architecture and describe their functions. What are the advantages of specifying not only the radio interface but also all internal interfaces of the GSM system?

4)(5.3): How do inclination and elevation determine the use of a satellite?

5)(7.5): If Bluetooth is a commercial success, what are the remaining reasons for the use of infra red transmissions for WLANs?

Other questions: For each question, each answer must not be written on more than two pages, i.e. on just one sheet!

6)This question is on Bluetooth.

  1. Name three important task for the master in a Bluetooth piconet. (3 cr)
  2. How is power saving issues handled in Bluetooth?(2 cr)
  3. How many actives slaves may there be in a Bluetooth picocell? (2 cr)
  4. In Bluetooth there may be packets of different length: 1-slot packets, 3-slot packets and 5-slot packets. Why is it so? (3 cr)

7)

  1. Frequency hopping is a widely used spread spectrum technique. Describe how it works. ( 2 cr)
  2. Describe slow and fast frequency hopping, respectively (2 cr)
  3. Describe the concepts of “short-term fading” and that of “long-term fading” and give examples of how they occur? (3 cr)
  4. Describe the concept of intersymbol interference(ISI) (3 cr)

8)

  1. The near/far effect is a severe problem of wireless networks using CDM. Describe this problem. (3 cr)
  2. Polling is an widely used media access technique. Describe this technique and give examples of systems where it is used. (4 cr)
  3. Figure 1 shows an example of how PRMA packet reservation multiple access scheme is used. Explain how it works. (3 cr)

9)

  1. A WLAN may be run in either infrastructure mode or in ad hoc mode. Describe the two modes. (3 cr)
  2. Give some examples of applications that are based on the ad hoc mode. (2 cr)
  3. The IEEE802.11 standard is widely used in WLANs. The MAC protocols used in this standard differ from those used in wired LANs. In wired LANs, i.e. in IEEE802.3 LANs (Ethernet) the main MAC protocol is CDMA/CD (Carrier Sence Multiple Access with Collision Detection). Why is that not a proper MAC protocol for WLANs? (5 cr)

10)

  1. Think of an operator running a GSM system in the 1800 MHz band. Throughout the years, this network has become more and more congested and the operator now is to increase the capacity of the GSM network. Give three examples of doing that. (5 cr)
  2. Now this operator wants to upgrade his GSM network to also handle GPRS traffics. Which elements are needed for that? Describe the role of these elements. (5 cr)
  3. After some years this operator wants to include UMTS in his network. What elements are needed for that? (5 cr)

11)For IEEE802.11 WLANs three different MAC protocols may be used. These are the BASIC DFWMAC-DCF using CSMA/CA, DFWMAC-DCF with RTS/CTS extension and DFWMAC-PCF with polling. Describe the three MAC protocols (15 cr)

Good Luck! --- Ulf

You need at least 43 cr in order to pass the exam.

54-64 cr => Give you a 4 on the exam

65 or more cr give you a 5 on the exam

Figure 1: