E4703 Wireless
Communications
Slide Set 9
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Announcement
•
Only half lecture today.
•
Afterwards, coffee/tea drinkers are invited to come
to the SIPA coffeeshop (118
th
& Amsterdam, 6
th
floor). My treat !
Outline
•
Summary of last lecture.
•
Spread Spectrum
¾
DirectSequence
¾
Frequency Hopping
•
Multiuser channels
•
Multiple Access: FDMA, TDMA, CDMA and
SDMA.
•
Random Access:
¾
Pure Aloha
¾
Slotted Aloha
¾
CSMA
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Summary of Last Lecture
•
Coding essential for reliable communication. Central
ingredient of any digital wireless system. It allows
reducing error probability (at rates below capacity) at the
expense of complexity and latency.
•
Studied
(
n
,
k
)
binary linear block codes, which map
blocks of
k
bits into codewords of
n
bits. Systematic if
the first
k
digits are the original information bits while
the last
(
n

k
)
are parity (redundancy) bits.
•
The Hamming distance between 2 codewords is the
number of digits in which they differ. The minimum
distance between any two codewords,
d
min
, is a key
parameter.