San Jose State University
Computer Engineering Department
CMPE 206 Spring 2011
Quiz 2 (type-a)
Full Name: _________________________ Grade ID___________________
Student Signature:______________________________________________________
1.-A channel has a bandwidth of 20[MHz]. If a two level signal is to be used for data
transmission, what is the maximum [Mb/sec] data rate such channel could support
assuming no significant noise level in the system.
Using the Nyquist Theorem (Chapter 2, page 94)
B = 20[Mhz], V=2, C=maximum data rate?
C = 2*B*log2V [bits/sec] = 2 * 20 * 106 * log2 2 [bits/sec] = 40 * 106 [bits/sec]
C= 40 [Mbits/sec]
2.- A framing system that uses bit-stuffing is sending frames of 100 bytes payload each.
For frames that have all bits set to one, what would be the payload overhead (as
percentage of payload) added by bit stuffing?
Each 5 bits will have to be followed by a stuffed 0 so if we have 100 bytes that is 800
bits and by dividing by 5 we get 160, so we have to stuff 160 bits and the overhead is
O=(160/800)*100%=20%
3.- Explain what a CRC is and why CRC is an efficient way to do error checking?.
CRC is a number of bits that make the data be divisible exactly by a well known
polynomial (by receiver and sender). Error checking is the reduced to dividing the
data at the receiver by the well known polynomial and making sure the reminder is
zero. If no remainder, the data is assumed error free, if the reminder is non-zero the
data is assumed incorrect and needs to be discarded. CRC are specially efficent
because they can be rapidly generated and checked in simple hardware.
4.- For the following data code, determine the minimum hamming distance and compute
the maximum number of bits in error that the code could correct. (Data bits are in bold,
underlined.
C1
0
0
1
0
1
C2
0
1
0
1
0
C3
1
0
0
0
0
C4
1
1
1
0
1
