Übungen zu Drahtlose Kommunikation. Wintersemester 2016/2017. Prof. Hannes Frey / Dr. Jovan Radak. Assignment 2

Size: px

Start display at page:

Download "Übungen zu Drahtlose Kommunikation. Wintersemester 2016/2017. Prof. Hannes Frey / Dr. Jovan Radak. Assignment 2"

Rosanna Manning
5 years ago
Views:

1 Übungen zu Drahtlose Kommunikation Wintersemester 2016/2017 Prof. Hannes Frey / Dr. Jovan Radak Assignment 2 voluntary submission until Sunday as PDF via mail to vnuml@uni-koblenz.de Name Address

2 Drahtlose Kommunikation WS 2016/17 Assignment 2 2/6 Exercise 1 Calculate the Fraunhofer distance for a 12cm long WLAN antenna that is operated at 5 GHz. What happens to the near field, when increasing the frequency and at the same time: 1) keeping the antenna length the same? 2) adjusting the antenna length according to λ/4? Exercise 2 The following formula is used for calculating the Doppler shift fd using velocity v and the wavelength λ: ff dd = vv λλ The Doppler shift is the difference between the original frequency f and the shifted frequency f' that is observed. The shifted frequency is calculated as follows, if the sender is moving cc towards the observer: ff = ff and the following, if the sender moves away from the observer: ff = ff cc vv (speed of light assumed to be: c = 3 * 10 8 m/s) Assume that a sender and a receiver, both operating at 900 MHz, are mounted on a vehicle driving with 100 km/h. At which frequency is the wave propagating in driving direction? cc cc+vv Assume the vehicle is directly heading towards a wall. The signal is reflected at the wall. At which frequency does the receiver mounted on the vehicle receive the reflected signal?

3 Drahtlose Kommunikation WS 2016/17 Assignment 2 3/6 Exercise 3 Given a scenario with three nodes: A, B and C. All have pairwise distance d=100m to each other (triangle). The channel behaves according to log-normal shadowing. The transmit power is PP tttt = , the PL coefficient is n=2,5 and the standard deviation is σσ = 55. For being able to correctly receive data, the received power PP rrrr has to be at least -80dBm. The PL at reference distance 1 m is PPPP(dd 00 = 1111) = (PL is Pfadverlust / Path Loss) What is the PL at distance d on average? Assume a receiver is located at distance d from a sender. Calculate the probability that the receiver is able to correctly receive data. c) When using multi-hop communication, not all pairwise links in the network need to be working. It is possible to route data multi-hop from node to node until they reach the destination. Thus, for multi-hop it is sufficient that there exists a working path between each pair of nodes. What is the probability that the nodes A, B and C are connected in terms of multihop communication? d) Each (single-hop) link should be working with a probability of 99%. How large must the distance d be chosen? Exercise 4 Research on the Internet how the different multiple access techniques (TDMA, SDMA, FDMA, CDMA) are applied to UMTS. Give one example for each multiple access technique.

4 Drahtlose Kommunikation WS 2016/17 Assignment 2 4/6 Exercise 5 Assume a two-ray ground model. The distance d between sender and receiver tends to infinity. But both nodes have a constant distance to the reflecting ground. Does the phase shift converge to a fixed value or does it periodically continue? Give a short explanation. Which channel models from the lecture are suitable for modeling the channel behavior in the following scenarios? Give a short explanation. 1) The receiver moves away from sender at constant velocity. 2) Sender and receiver move at same speed into the same direction. 3) Sender and receiver are not moving. Exercise 6 What limits the maximal number of concurrently active terminals in a system in which the following multiple access / multiplexing scheme is used: 1) TDMA : 2) FDMA : 3) CDMA : Cell breathing describes the effect in CDMA systems that the radius of a cell can change. Describe briefly when and why the radius is decreasing or increasing.

5 Drahtlose Kommunikation WS 2016/17 Assignment 2 5/6 Exercise 7 Sketch the missing signals for even and odd bits and the resulting MSKmodulated signal into the diagram below. Use the modulation scheme shown here on the right-hand side:

6 Drahtlose Kommunikation WS 2016/17 Assignment 2 6/6 Exercise 8 Given is a fictitious constellation diagram: How many different values does this constellation diagram use for: 1) Amplitude 2) Phase 3) Frequency How many bits are encoded into one symbol? c) Why is this constellation diagram inefficient? d) Specify the values of amplitude and phase of the symbol that is tagged with an (x) in the upper right corner.

Übungen zu Drahtlose Kommunikation

Übungen zu Drahtlose Kommunikation Wintersemester 2016/2017 Prof. Hannes Frey / Dr. Jovan Radak Assignment 1 voluntary submission until Wednesday 2016-11-23 as PDF via mail to vnuml@uni-koblenz.de Name