• Tín hiệu truyền qua kênh truyền sẽ bị ảnh hưởng bởi
nhiễu, can nhiễu, fading… là tín hiệu đầu thu bị sai.
• Mã hóa kênh: dùng để bảo vệ dữ liệu không bị sai
bằng cách thêm vào các bit dư thừa (redundancy).
• Ý tưởng mã hóa kênh là gởi một chuỗi bit có khả
năng sửa lỗi
• Mã hóa kênh không làm giảm lỗi bit truyền mà chỉ làm
giảm lỗi bit dữ liệu (bảng tin)
• Có hai loại mã hóa kênh cơ bản là: Block codes và
Signal detection in AWGN channels
Minimum distance detector.
Average probability of symbol error.
Union bound on error probability.
Upper bound on error probability based
on the minimum distance.ISI in the detection process due to the
filtering effects of the system
Overall equivalent system transfer function
Convolutional codes are linear.
Therefore, the Hamming distance between any pair of code sequences corresponds to the Hamming
distance between the allzero
code sequence and some nonzero code sequence. The nonzero sequence of minimum Hamming weight diverges from the allzero
path at some point and
remerges with the allzero
path at some later point
My objective in writing this book was to produce a general, comprehensive textbook that treats all the
essential core areas of cryptography. Although many books and monographs on cryptography have been
written in recent years, the majority of them tend to address specialized areas of cryptography. On the
other hand, many of the existing general textbooks have become out-of-date due to the rapid expansion
of research in cryptography in the past 15 years.
Pandemic planning should consider the need for stockpiling of essential supplies.
Discuss with key suppliers a plan for regular shipments in the event of shortages or
disruptions in transportation systems.
Shortages may occur because of disruptions in transportation systems or inability of
suppliers to meet demands because of their own staff shortages. Canadian supplies
travel long distances by truck, train and aircraft and are vulnerable to any disruption.
Weighted graph We can add attributes to edges, We call the attributes weights; Then if we want the shortest travel distance between cities an appropriate weight would be the road mileage; If we are concerned with the dollar cost of a trip and went the cheapest trip then an appropriate weight for the edges would be the cost to travel between the cities.
For reliable communications to take place on a network, things like the physical method of signaling and the meaning of each signal or series of signals must be defined ahead of time. Create a simple physical network and agree on some basic rules for communication in order to send and receive data. This will be a digital network based on the American Standard Code for Information Interchange (ASCII). It will be similar to the old telegraph Morse code-based systems. In these older systems the only means of communicating over long distances was by sending a series of dots and dashes...
Matched decoding is a technique that enables the efficient maximum-likelihood sequence estimation of convolutionally encoded PAM-transmission over ISI-channels. Recently, we have shown that the super-trellis of encoder and channel can be described with significantly fewer states without loss in Euclidean distance, by introducing a non-linear representation of the trellis. This paper extends the matched decoding concept to punctured convolutional codes and introduces a time-variant, non-linear trellis description.