ECE 5930 / 6930 Wireless Communication

Midterm I

 

October 3, 2001

 

 

Name _______________________________________

 

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

 

 

____  ECE 5930

 

 

____ ECE 6930

 


  1. (33 points)  Capacity/co-channel interference/cell splitting and sectoring

 

    1. How many users can a blocked-calls-dropped system support with 20 channels and a required grade of service that drops less than 10 calls per thousand?  The average call lasts 30 seconds, and the average user makes 1 call per hour.
    2. For a cluster size of 7, will the S/I be sufficient for a TDMA system (15dB required) in downtown New York City?
    3. If each cell is 1km in radius, use the log-distance model to determine how much power (measured at 1 meter from the base station antenna) the base station  must transmit if the phone can receive –100dB of power?
    4. Explain how your answers to (a-c) will change if you use cell splitting or sectoring:  (circle the correct answers)

 

 

Cell Splitting    

Cell Sectoring

# of users U

Decrease

NoChange

Increase

Decrease

NoChange

Increase

S/I       

Decrease

NoChange

Increase

Decrease

NoChange

Increase

Ptx

(basestation)           

Decrease

NoChange

Increase

Decrease

NoChange

Increase

 


  1. (33 points)  Large Scale Path Loss

 

Given: 

            Height of basestation transmitter            100 meters

            Height of receiving antenna                    2 meters

            Frequency                                            1900 MHz

            Distance  between TX and RX  1 km

            Sensitivity of the phone             -100 dB

            Maximum power of the phone   1 Watt

            Losses in the basestation receiver          5 dB

            Gain of basestation antenna                   5 dBi

            Gain of phone antenna              1.6 dBi

Environment:

      USU campus, including buildings and trees.

 

a.       Evaluate the following models for determining the path loss between phone and basestation.  Explain the limitations of each model for this application:

 

Friis transmission equation

 

Ground Bounce Model

 

Reflection Model

 

Log-Distance Model

 

Okumura Model

 

Hata Model

 

b.      Using the Okumura model, prepare a link budget to determine the power received by the basestation when the phone is transmitting.   Neglect losses not given above or indicated in your model.

 

c.       Explain “path balance” and why it is important.

 


  1. (15 points) Small Scale Fading

 

    1. Both Log-Distance and Raleigh models are used to compute received power in multipath environments.  A link budget commonly includes losses predicted by BOTH of these models. 

 

Explain why.

 

 

 

 

What value(s) obtained from the Raleigh distribution of data should be included in the link budget losses?

 

 

 

 

 

    1. For a line-of-sight application, should you use Raleigh or Ricean statistics? 

 

    1. For Ricean scattering, should K be larger in a hallway or under the breezeway?

 

  1. (19 points) Cellular systems

 

A mobile user is traveling 60 mph when his call is handed from one basestation to another.  The call is accidentally disconnected.  List at least five different things that could have gone wrong.
ECE 5930/6930 Midterm I

 

Name ________________________________

 

 

Problem 1  __________ / 33 points

 

Problem 2  __________ / 33 points

 

Problem 3  __________ / 15 points

 

Problem 4  __________ / 19 points

 

Total          __________ / 100 points