3 Shannon Capacity Defined as the maximum mutual information of channel Maximum error-free data rate a channel can support.Theoretical limit (usually don’t know how to achieve)Depends on the channel characteristicsWe focus on AWGN channel with fadingOmar Abu-Ella
9 Shannon Limit in AWGN channel What is the minimum SNR per bit (Eb/N0) for reliable communications?Omar Abu-Ella
10 Capacity of Flat-Fading Channels Capacity defines theoretical rate limitMaximum error free rate a channel can supportDepends on what is known about channelCSI: channel state informationCDI: channel distribution informationUnknown fading:Worst-case channel capacityFading Known at Receiver OnlyOmar Abu-Ella
19 Performance Comparison At high SNR, water-filling does not provide any gain.Transmitter knowledge allows rate adaptation and simplifies coding.Omar Abu-Ella
20 Channel 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 optimalOmar Abu-Ella
21 Frequency Selective Fading Channels For time-invariant channels, capacity achieved by water-filling in frequencyCapacity of time-varying channel unknownApproximate by dividing into subbandsEach subband has width Bc (like MCM).Independent fading in each subbandCapacity is the sum of subband capacities1/|H(f)|2BcPfOmar Abu-Ella
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