Homework 5 - Association and Handover (Chapter 8)
Mobile Networks
Exercise 1. Example 8.7 from the course book [1] presents the following scenario. Assume a
straight highway with 8 km length. Traffic intensity follows a location-dependent Poisson distribution with the intensity
8
2
>
if 0  x < 2
<x
x
⇢(x) = 4 2 if 2  x  8
>
:
0
otherwise
For deploying two base stations that cover the highway, Example 8.7 shows how to estimate the
position z of the handover point so that the traffic load is equally distributed between the two base
stations. This example assumes that the propagation loss is distance dependent and fading e↵ects
are neglected. The result is z = 3.17 km. Using this information, do the following:
A. Example 8.7 assumes that z lies between 2 and 8 (i.e., 2  z  8). Using the same procedure
described in Example 8.7, examine the case where z lies between 0 and 2 (i.e., 0  z  2)
and demonstrate that a feasible solution does not exist in this case.
B. Let us now find the best possible location of the right base station (located somewhere between
z and 8). In this example, we consider only the downlink. We want to find the location of the
base station such that the overall power radiated by the base station can be kept minimal.
Use the traffic intensity distribution presented above as an approximation of the number of
terminals in a particular location. Assume the terminals to be static. Refer to the SNR
equation below, and assume that the propagation exponent ↵ is equal to 2. (hint: the base
station should be placed in such a way that the weight of the traffic of all terminals at its left
is equal to the weight of those placed at its right).
=
c t Pt
,
r↵ N
r is the distance from receiver to base station
Pt is the transmitted power
N is the noise power
ct is the antenna constant
↵ is the propagation constant
1
where:
226
Figure 8.19
Exercise 2 (Exercise 8.5 from course book [1]). Cellular CDMA systems employ soft handover for both coverage and link reliability. A mobile receiver within an IS-95 system has been
communicating for a while and receives the pilot signals shown in Figure 1. We assume that this
Association
andishandover
mobile receiver
in soft handover and your task is to identify the set of cells that are in the active
set of the mobile unit at time ⌧ = ⌧0 . The handover drop time is 10 seconds and the handshaking
time between the base station and the mobile can be neglected.
Pilot
Eb
I0 p
Cell 1
Cell 2
TADD
TDROP
Cell 3
Cell 4
Cell 5
Cell 6
τ0
τ in seconds
Channel variations.
Figure 1: Channel variations
References
A. Going through each pilot signal, identify the status (in the active set, candidate set or neighbor
set) of each
signal at
⌧0 . Clearly
explain
J. G. Andrews,
H.pilot
Claussen,
M.time
Dohler,
S. Rangan
andyour
M. results.
C. Reed. 2012. Femtocells: past,
present,
andthe
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B. Deduce
set ofIEEE
cells Journal
that are on
in the
activeAreas
set of in
theCommunications,
mobile unit at time
⌧0 . 497–508.
O. Grimlund and B. Gudmundson. 1991 (May 19–22). Handoff strategies in microcellular
systems. Pages 505–510 of: Proc. 41st IEEE Vehicular Technology Conference (VTC).
References
M. Gudmundson. 1991a (May). Analysis of handover algorithms. Pages 537–542 of: 41st IEEE
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