Announcements Schedule changes next week No lecture next Tues 23 Makeup class Wed 25 11301250pm wlunch in Gates B03 Project proposals due 27 I can provide early feedback MT week of 217 68pm pizza after poll this week details ID: 798899
Download The PPT/PDF document "EE359 – Lecture 8 Outline" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
EE359 – Lecture 8 Outline
Announcements
Schedule changes next week
No lecture next Tues 2/3.
Makeup class: Wed 2/5 11:30-12:50pm w/lunch in Gates B03
Project proposals due 2/7; I can provide early feedback
MT week of 2/17, 6-8pm (pizza after), poll this week; details
soon
New version of Reader with Chapters 1-7 available next week
Capacity of Fading channels
Recap
Optimal Rate/Power Adaptation with TX/RX CSI
Channel Inversion with Fixed Rate
Capacity of Freq. Selective Fading Channels
Linear Digital Modulation Review
Performance of Linear Modulation in AWGN
Slide2Review of Last Lecture
Channel Capacity
Maximum data rate that can be transmitted over a channel with arbitrarily small error
Capacity of AWGN Channel: Blog2[1+g] bpsg=Pr/(N0B) is the receiver SNRCapacity of Flat-Fading ChannelsNothing known: capacity typically zeroFading Statistics Known (few results)Fading Known at RX (average capacity)
Slide3Review of Last Lecture (
ctd
)
Capacity in Flat-Fading: g known at TX/RXOptimal Rate and Power AdaptationThe instantaneous power/rate only depend on p(g) through g0
1
g
g
0
g
Waterfilling
Same result with equality
Slide4Channel Inversion
Fading inverted to maintain constant SNR
Simplifies design (fixed rate)
Greatly reduces capacityCapacity is zero in Rayleigh fadingTruncated inversionInvert channel above cutoff fade depthConstant SNR (fixed rate) above cutoffCutoff greatly increases capacityClose to optimal
Slide5Capacity in Flat-Fading
Rayleigh
Log-Normal
AWGN capacity
l
ower than
w/fading
u
nder TX/RX CSI
AWGN
TX/RX CSI
RX CSI
Truncated Inversion
Inversion
AWGN
TX/RX CSI
RX CSI
Truncated Inversion
Inversion
Slide6Frequency Selective
Fading Channels
For time-invariant channels, capacity achieved by water-filling in frequency
Capacity of time-varying channel unknownApproximate by dividing into subbandsEach subband has width Bc (like MCM/OFDM).Independent fading in each subbandCapacity is the sum of subband capacities
B
c
f
P(f
i
)
1/|H(f)|
2
f
i
1/
g
0
1/|
H(f
i
)|
2
Total Power
Slide7Review of Linear
Digital Modulation
Signal over
ith symbol period:Pulse shape g(t) typically NyquistSignal constellation defined by (si1,si2) pairsCan be differentially encodedM values for (si1,si2)
log2 M bits per symbol P
s
depends on
Minimum distance
dmin (depends on
gs)# of nearest neighbors aMApproximate expression: Standard/alternate Q function
Slide8Main Points
Channel inversion practical, but should truncate or get a large capacity loss
Capacity of wideband channel obtained by breaking up channel into
subbandsSimilar to multicarrier modulationLinear modulation dominant in high-rate wireless systems due to its spectral efficiencyPs approximation in AWGN:Alternate Q function useful in diversity analysis