LUNDS TEKNISKA HÖGSKOLA

Inst. för telekommunikationssystem

Tentamen i AVANCERAD TELEKOMMUNIKATION, 2007-05-30

Tid: 08.00 – 13.00

Write clear!

Write your name an all the sheets you hand in!

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Questions from the book:

  1. What are the main benefits of a spread spectrum system? How can spreading be

achieved? (2.13) (3 cr)

  1. Explain the term interference in the space, time, frequency, and code domain. What

are countermeasures in SDMA, TDMA, FDMA, and CDMA systems? (3.8) (3 cr)

  1. Why are so many different identifiers/addresses (e.g., MSISDN, TMSI, IMSI) needed

in GSM? Give reasons and distinguish between user related and system related

identifiers. (4.16) (3 cr)

  1. Why are GEO systems for telecommunications currently being replaced by fibre

optics? (5.2)

How do inclination and elevation determine the use of a satellite? (5.34) (3 cr)

  1. In what situations can collisions occur in IEEE802.11, HiperlanII and Bluetooth respectively? Distinguish betweencollisions on PHY and MAC layer. How do the three wireless networks try to solve thecollisions or minimize the probability of collisions? (7.12) (3 cr)

Other questions:

  1. Describe the main principles behind SPREAD SPECTRUM techniques. Describe the two different spread spectrum techniques that are presented in this course. (10 cr)
  1. a)Think of a cellular system like GSM system. With a given cell structure, the system can handle a certain number of calls at any time. How can we increase the capacity in terms of serving customers in a certain geographical part of the system? How can we increase the total capacity of the whole system? (5 cr)

b) Cellular systems have proven to be very effective. Give three advantages of cellular systems with small cells compared to cellular systems with large cells. (5 cr)

  1. a) Bluetooth offers two different types of links, a synchronous connection-oriented link (SCO) and an asynchronous connectionless link (ACL). Describe the two types of links.(4 cr)

b) Give a scenario where it is better to connect two devices via Bluetooth compared to connect them via a WLAN based on IEEE802.11. Give two reasons why it is better to connect these devices via Bluetooth instead of via a WLAN. (3 cr)

c) How is power management implemented in Bluetooth? (3 cr)

  1. a) What are the general problems of satellite signals travelling from a satellite to a receiver? (3cr)

b)Think of a mobile system based on satellite communications. What are the benefits contra drawbacks with such a system compared a land based GSM/GPRS system? (3cr)

c)2G and 3G systems can both transfer data. Compare these approaches with DAB/DVB and list the reasons for and against the use of DAB/DVB. (4cr)

  1. a) Figure 1 illustrates the use of RTS and CTS in an IEEE802.11 network. Here the MAC algorithm is DFWMAC-DCF with RTS/CTS extension. Describe how this MAC algorithm works and also the purpose of the DIFS and SIFS. What is the NAV (RTS) and NAV (CTS)? (8 cr)

b) Figure 2 shows the contention-free access using polling mechanisms (PCF) in an IEEE802.11 WLAN. Can we use this MAC-scheme both for an infrastructure based network as well as for an ad hoc based network? Give a good motivation to your answer. Describe what you see in the figure. (7 cr)

  1. a) Think of an operator that has a GSM system. What is needed to enhance this system to a combined GSM/GPRS system. When this is done, what is needed to enhance this system to a combined GSM/GPRS/UMTS system?(5 cr)

b)Describe the concept of “PDP Context” in a GPRS system. Which parameters are set up in the PDP Context? Where is the PDP Context stored? (5cr)

c)GPRS can provide Quality of Service within the GPRS network. There are four parameters that can be set when it comes to QoS here. Which are they? (5cr)

Good luck!

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

Figure 2

Figure 3

Figure 4

Fill in figures 5 and 6 to show your answers to question 11!

Figure 5

Figure 6

Fill in Figure 7 below to show your answers to question 7a!

Figure 7