LAB-5
Wireless Networks
Question No 1:
What is the period of the Moon, according to Kepler’s law?
Solution:
Here C is a constant approximately equal to 1/100. The period is in seconds and the distance in
kilometers.
Reference: Behrouz Forouzan 5th edition: page No 483,484
Replace the radius of the earth to 6371 instead of 6378
Question No 2:
According to Kepler’s law, what is the period of a satellite that is located at an orbit
approximately 35,786 km above the Earth?
Solution:
Reference: Behrouz Forouzan 5th edition: page No 483,484
Replace the radius of the earth to 6371 instead of 6378
Question No 3
We want to put a satellite in a circular orbit at 500 km above the surface (LEO Orbit).What will
be the speed of rotation required. Given the following:
𝐆 = 𝟔. 𝟔𝟕 × 𝟏𝟎−𝟏𝟏
𝐑 = 𝐑𝐚𝐝𝐢𝐮𝐬 𝐨𝐟 𝐭𝐡𝐞 𝐞𝐚𝐫𝐭𝐡 = 𝟔𝟑𝟕𝟏 𝐊𝐦 = 𝟔𝟕𝟑𝟏𝟎𝟎𝟎𝐦
𝐌𝐚𝐬𝐬 𝐨𝐟 𝐞𝐚𝐫𝐭𝐡 𝐌 = 𝟓. 𝟗𝟖 × 𝟏𝟎𝟐𝟒 𝒌𝒈
Solution:
𝑣=√
𝐺𝑀
𝑟
Where r=distance from the center of earth=6731+500=7231 Km=7231000m
𝟔. 𝟔𝟕 × 𝟏𝟎−𝟏𝟏 ∗ 𝟓. 𝟗𝟖 × 𝟏𝟎𝟐𝟒 𝑚
𝑣=√
( )
7231000
𝑠
Question No 4:
From the following graph, explain the relationship
between the satellite parameters, Coverage, Period
and Delay with the orbital height of the satellite.
Solution:
We can see from the figure that with an increase in the orbital height, the coverage area, Period
of rotation and the delay increases.
Reference William Stallings: Wireless Communication and Networks second edition Page 241
Question No 5:
From the following curve, Explain the relationship between the capacity with the number of
accesses or channels for FDMA and TDMA.
Solution:
Note the dramatic drop in capacity of FDMA as the number of channels increase. By contrast,
TDMA drops much more slowly as the number of time slots (channels) increase
.
Reference William Stallings Wireless Communications and networks: Second Edition Page 259
Channelization
Question 1: Find the chips for a network with
a. Two stations
b. Four stations
Solution:
We can use the rows of W2 and W4 in the figure
a. For a two-station network, we have [+1 +1] and [+1 −1].
b. For a four-station network we have [+1 +1 +1 +1], [+1 −1 +1 −1], [+1 +1 −1 −1], and
[+1 −1 −1 +1].
Question No 2: What is the number of sequences if we have 90 stations in our network?
The number of sequences needs to be 𝟐𝒎 . We need to choose m = 7 and N = 27 or 128. We
can then use 90 of the sequences as the chips.
Question No 3: Prove that a receiving station can get the data sent by a specific sender if it
multiplies the entire data on the channel by the sender’s chip code and then divides it by the
number of stations.
Solution:
Let us prove this for the first station, using our previous four-station example. We can say that
the data on the channel D = (d1 ⋅ c1 + d2 ⋅ c2 + d3 ⋅ c3 + d4 ⋅ c4). The receiver that wants to get
the data sent by station 1 multiplies these data by c1.
We then divide by N we get d1.
Reference: Behrouz forouzan: Fifth Edition: Chapter 12, Page 350 and 351