1.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.
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?
2.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.
3.a. An MFSK modulation scheme has 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 FHSS scheme is used in conjunction with an MFSK scheme that hops among four different carrier frequencies. What is the number of possible frequency assignments? List the possible frequency assignments.
4. 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.
5.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.
6. 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?