Assignment

Question 1.

Describe the significance of the Nyquist criterion for ISI cancellation. Compare and contrast the various filtering techniques for minimizing the effects of ISI.

Question 2.

a. Briefly describe the concept of spread spectrum technique and list three important benefits.

b. Assume we wish to transmit a 64-kbps data stream using spread spectrum technique. Compute the bandwidth required for SNR = 0.1 and 0.01.

c. If the data stream is transmitted using a bandwidth of 64 kHz in an ordinary system (without spread spectrum), what is the SNR that could be tolerated without experiencing significant errors?

Question 3.

a. What is frequency hopping spread spectrum? Explain the difference between slow FHSS and fast FHSS.

b. Calculate the minimum number of PN bits required for each frequency hop for an FHSS system that employs a total bandwidth of 800 MHz and an individual channel bandwidth of 200 Hz. If this system uses MFSK modulation in conjunction with FHSS, calculate the processing gain.

Question 4.

a. An MFSK modulation scheme with M = 4has a carrier frequency of 250 kHz, a difference frequency of 25 kHz, and two bits per signal element. Make a frequency assignment for each of the possible data combinations.

b. This MFSK scheme is used in conjunction with an FHSS scheme that hops among 4 different carrier frequencies. What is the number of possible frequency assignments? List the possible frequency assignments.

Question 5.

a. Describe the key features of the FDMA technique and identify a cellular operator that uses this multiple access technique.

b. A cellular operator using the FDMA technique is allocated a total spectrum of 25 MHz. The system has a channel bandwidth of 60 kHz. It also uses a guard band of 20 kHz. Compute the number of channels that can be simultaneously supported in this wireless system.

Question 6.

a. The U.S. Digital Cellular provider uses a TDMA scheme for multiple access. It uses a 48.6 kbps data rate and supports three users per frame. Each user occupies two of the six time slots per frame. Compute the raw data rate provided for each user.

b. If the frame efficiency is 75% and if the time duration of a frame is 6 ms, compute the number of information bits sent to each user per frame.

c. If six users per frame are supported using half-rate speech coding, compute the information rate per user.

Question 7.

a. Describe the important criteria that needs to be considered for the generation of spreading sequences in spread spectrum techniques.

b. Describe the significance of the terms autocorrelation and cross correlation as applied to the generation of spreading sequences for spread spectrum.

c. Compare and contrast the two general categories (PN sequences and orthogonal codes) for generating spread spectrum.

Question 8.

a. Describe the operation of the CDMA technique.

b. In a CDMA system, user A transmits using the Walsh code (-1 1 -1 1 -1 1 -1 1) and user B transmits using the Walsh code (-1 -1 11 -1 -1 1 1), respectively. Show the output at the receiver if A transmits a data bit 0 and B transmits a data bit 0. Do you think whether the receiver is capable of correctly identifying a data bit 0 transmitted by user A?

Question 9.

What is pulse shaping? What are the benefits of pulse shaping?

Question 10.

Multiple Access Techniques allow several users to share the radio spectrum. Identify the various multiple access techniques and associate them with different wireless communication systems.