Chapter 1

Chapter: 1

1.      Explain in details about various channel assignment strategies.

2.      Explain the following terms with respect to wireless networks:

a.       Frequency Reuse

b.       Co-channel interference

c.        Handoff

d.      Umbrella cell approach

e.       Dwell time

f.       Cell dragging

g.      Cluster

h.      MAHO

i.         Channel Capacity

j.        Differentiate between Hard hand off and Soft handoff.

3.      Why is hexagonal cell shape preferred over square or triangular cell shape to represent the cellular architecture

4.      Calculate the total available channels for a cellular system having a total bandwidth of 60MHz which uses two 50 kHz simplex channels to provide full duplex voice and control channels. Assume that the system has nine cell reuse pattern and 1 MHz of the total BW is allocated for control channels, determine an equitable distribution of control channels. Also calculate the number of the control channels and voice channels/cell. Assume the area of the cell is 9 Sq Km and the area of the entire system is 3630 Sq Km. If the cluster size is reduced to 4, what is the system capacity. Comment on this.

5.      A cellular service provider decides to use a digital TDMA scheme which can tolerate a signal-to-interference ratio of 15 dB in the worst case. Find the optimal value of N for (a) omni directional antennas, (b) 120* sectoring, and (c) 60* sectoring. Should sectoring be used? If so, which sectoring (120* or 60*) will be better? Assume a path loss exponent n=4.

6.      Prove that for a hexagonal symmetry,the co-channel reuse ratio is given by Q=(3N)^1/2.

7.      Illustrate the principle of cell splitting in a cellular system. Prove that the transmit power of the microcell must be reduced by 12 dB in order to fill in the original coverage area with microcells, while maintaining the S/I requirement for the path loss exponent n=4.

8.      For a seven cell reuse pattern and hexagonal cell geometry show that 120* sectoring improves signal to interference ratio by about 5 dB.

9.      A cellular system has 32 cells; each cell has 1.6 km radius and the system reuse factor of 7. The system is to support 336 traffic channels in total. Determine the total geographical area covered, the number of traffic channels per cell and total number of simultaneous calls supported by this system.

10.  Assuming six co-channel interfering cells, find the S/I ratio for path loss co-efficients of n=3 and n=4. Consider cluster size N=7. In which case 15 dB requirement is met?what needs to be changed to meet the same condition in second case?

11.  For a regular cellular structure with equal size hexagonal cells, show that D/R= (21) ½ , Where D is the minimum distance between the centers of adjacent cells and R is the radius of each cell. Assume 7-cell reuse pattern.

12.  Compare the S/I ratio for a mobile radio for the following cases of cellular system with frequency reuse factor of 7 for (i) Omni directional antenna (ii) 120* Directional antennas.

13.  Consider two different cellular systems that share the following characteristics. The frequency bands are 825-845 MHz for uplink and 870-890 MHz for the downlink. A duplex circuit consists of one 30 kHz channel in each direction. The systems are distinguished by the reuse factor, which are 4 and 19 respectively. For these systems, (i) Find the number of simultaneous communications that can be supported by a  single cell in each system. (ii) Suppose that in each systems the cluster of cells (4,19) is duplicated 16 times, find the number of simultaneous communications that can be supported by each system. (iii)Suppose the average user makes 6 calls per 24 hours and mean call duration is 6 minutes, estimate the total number of users that can be supported by each system. (iv) If the billing for each customer is at the rate of 50 paisa/minute, determine average revenue per user (ARPU).

14.  Derive the expression for S/I ratio for adjacent channel interference for cellular systems.

15.  Derive an expression for a ground reflection model assuming distance between transmitter and receiver antenna is very large compare to heights of the antennas.

16.  The received power at a distance of 100 km is 5 nw for a communication link. Determine the received power at a distance 200 km for the same link. Assume free space propagation mechanism.

For a seven cell reuse pattern and hexagonal cell geometry show that 120 sectoring improves signal to interference ratio by about 5 dB.