Telcom 2700 Wireless Networks Midterm Study Notes
The midterm exam will cover the set of Slides (1-9). This includes the five homework assignments. The exam is open book and notes. The format of the exam will be a mix of short answer questions and one or two problems similar to the homework. Please bring a calculator and the Erlang tables from class.
Examples of short answer questions include questions 1 and 2 from Homework 1, questions 1 and 4 from Homework 2, question 4 from Homework 3, and questions 1, 2 and 5 on Homework 4, any of the sub-questions (i.e., (a), (b), etc.) of questions 1 and 2 from Homework 5. Some examples from old exams
1. Briefly describe the difference between the following
(a) Fast Frequency Hopping Spread Spectrum and Direct Sequence Spread Spectrum
(b) Inter-VLR and Intra-VLR location update in tracking a mobile GSM user
- How is authentication achieved in GSM? Why are the phone calls encrypted?
3. Digital cellular systems employ both speech coding and error control coding in the transmission of voice information. (a) What is the purpose of each type of coding? (b) How does each affect speech quality? (c) How does each affect the bandwidth required?
- The near –far problem is a major concern in IS-95 (cdmaone) systems, why is this less of an issue in GSM and AMPS?
Examples of problem questions include any single part (i.e., (a), (b), (c)) of questions 4 from Homework 1, questions 1 and 3 from Homework 3, question 4 from Homework 4. Examples from past exams include
1. Assuming a free space loss environment, a 1 watt transmitter for each direction and a distance of 3 Km, determine the difference in the path loss between the uplink and the downlink of AMPS channel 1.
2. Consider a AMPS cellular system operating in the A Band with 7 cells covering an area of 3100 km2 . The traffic in the seven cells is as follows
Cell # / 1 / 2 / 3 / 4 / 5 / 6 / 7Erlangs / 30.8 / 66.7 / 48.6 / 33.2 / 38.2 / 37.8 / 32.6
The average user in the system generates .03 Erlangs of traffic in the busy hour and the system is designed for a grade of service of 2% call blocking.
(a) Determine the number of subscribers in cell 1 and 6
(b) Determine the number of traffic channels required in cell 1 and 6
5.Frequency reuse is a basic concept in mobile phone systems.
(a) You are operating a cellular network with 30 KHz AMPS traffic channels 1 through 12 and control channels {313, 317, 321, 325}. Labeling the traffic channels as {f1, f2, f3, f4, f5, f6, f7, f8, f9, f10, f11, f12} and the control channel as {c1, c2, c3, c4}. Place the traffic and control channels in the cells below such that a frequency reuse cluster size of 4 is used.
(b) If each user makes 2 phone calls of 3 minutes duration in the busy hour , how many users can be supported in each cell while maintaining a call blocking rate of 5%
5. A GSM subscriber whose home base is Pittsburgh and is registered there, travels to Paris and turns on their phone in order to receive a call. With reference to the MSC, VLR, HLR, and AUC explain how location tracking is done