Name ______________________________

Email:

You may use your portfolio and a calculator but no textbook.

Please remember:

1) Turn in portfolio to the ECE office.

2) Turn in 3 labs to me (Raleigh/Rician, BPSK/Eye Diagrams, CDMA)

3) Email final paper to:  furse@ece.usu.edu

Thank you! I have enjoyed having you in my class.  Have a great break!

1. (Midterm I – 33 points) 

1. Suppose that you have a communication system with a cluster size of 12 and a path loss exponent of 4.     What will be the signal to interference ratio?    S/I = ____________

2. If  TWO of the cells in the cluster in part (a) are turned off (broken, not in use, etc.),

what is the S/I = ____________?

c.   For Cellular USU (a new cell phone company J), a typical student makes 1 call per hour (between classes), and the average call lasts 15 minutes.    How many Erlangs is each student using?   ________________ Erlangs

4. Cellular USU owns 200 cells.  Each cell has 15 channels.  Calls that are blocked are held (not dropped) until a channel becomes available.  The company advertises that “You will have to wait only once in a hundred calls.”  How many student customers can Cellular USU support?  __________

5. One of the new engineers hired by Cellular USU does not think the system will work properly, because all USU classes finish at the same time, and therefore everyone is trying to call at the same time. 

Is there a problem?  Yes / No          If yes, what can Cellular USU do about it?
2. (Midterm I – 33 points) 

1. Cellular USU is going to transmit from the stadium to the engineering building (0.25 km).  Two student engineers are hired to measure the log-distance path loss exponent (n).  They are given a spectrum analyzer (that measures POWER in dB) and a signal generator (that outputs a sine wave).  Write an instruction manual below that tells the students what to do to find the path loss exponent:

b. The Cellular USU specifications are given below.  The transmitter is inside the USU radio station.

How much power should the base station transmitter output in order to get a suitable signal to the mobile?    Power Transmitted =    ____________ Watts

Also, Indicate what data is needed for the calculation:

Cable loss from TX to base station antenna                               5 dB                 needed / not needed

Reflection coefficient at base station antenna                              1 dB                 needed / not needed

Gain of the base station antenna                                                12 dBi              needed / not needed Sensitivity of the receiver chipset INSIDE the mobile             -115 dBm        needed / not needed

Power transmitted by the mobile                                               1W                  needed / not needed

Gain of the mobile antenna                                                        2 dBi                needed / not needed

Reflection coefficient inside the mobile                           4 dB                 needed / not needed

Loss due to the head                                                                 3 dB                 needed / not needed

3. (Midterm I – 33 points) Cellular USU wants to ensure that their system works inside the TSC building.  The students have been asked to determine the effect of small scale fading on the system performance.

a) The students need to determine if transmission into the Hub dining area (which has lots of windows but is shaded by concrete overhangs) is Raleigh or Rician.  They can see the transmitter from the dining area.  One student argues that it is Raleigh, and the other argues that it is Rician. Who is right and why?

b) The students measure the power within the Hub, and find that the average is -90 dBm.  They need to determine what percent of the area in the Hub will have power below -100 dBm.  They have a spectrum analyzer (to measure power) and signal generator.  Write a set of detailed instructions for them to do this.

4. (Midterm II – 33 points) For a frequency-hopped CDMA system, the digital data and PN code are shown below.  Each digital data bit lasts 1 second.

Digital Data                  1                      0                      1                     

PN code                      110101            100111            010001           

Time                             1 sec                2 sec                3 sec               

a. What is the processing gain?  Gp = ______________

2. Sketch the transmitter for the system, and explain how it works.

3. The system uses FOUR different frequencies, and the lookup table below gives the code for each frequency.  Write an equation for the signal that will be output by the transmitter:

Code	Frequency
00	F1
01	F2
10	F3
11	F4

Time	Transmitted signal
1 sec
1.5 sec
2 sec
2.5 sec

5. (Midterm II – 33 points)

Given a CDMA IS-95 system:

            Blocked calls are dropped

            Blocking probability                  1%

            Students are transmitting data 100% of the time (no breaks, cell phone video!)

            Other cell interference factor     0.5

            CDMA chip rate                      1.23 MHz (IS-95)

            Data rate                                  9600 baud

            (E_b / I_t ) _reqd = 7 dB

            1/h = 10

            Power control is perfect.

a. How many users can one cell support ? ____________________

b. One user (who is an electrical engineer) figures out how to increase the power transmitted by his phone significantly. 

Does that user experience better or worse reception?  Better / Worse

Do the other users experience better or worse reception?  Better / Worse

WHY?

6. (Midterm II – 33 points) 

1. Compare and Contrast analog and digital modulation:

	Analog	Digital
Advantages
Disadvantages

2. For a BPSK signal using a raised cosine pulse, sketch the eye diagram.  Show what happens to the eye diagram when the following problems occur in the system:

(1) Perfect System

(2) White Gaussian Noise is added.

(3) Sampling Jitter causes sampling at the wrong time

(4) Synchronization error

(5) Poor power control

(6)