Adaptive Modulation and Coding: Master Universitario en Ingenier Ia de Telecomunicaci On
Adaptive Modulation and Coding: Master Universitario en Ingenier Ia de Telecomunicaci On
Adaptive Modulation and Coding: Master Universitario en Ingenier Ia de Telecomunicaci On
I. Santamarı́a
Universidad de Cantabria
Introduction Rate adaptation Power adaptation Adaptive coding Hybrid techniques
Contents
Introduction
Rate adaptation
Power adaptation
Adaptive coding
Hybrid techniques
Introduction
Goal: to adapt the transmitted power, constellation size, and/or
coding technique in order to maintain
Esquema a given fixed instantaneous
general
BER for each symbol while maximizing the average data rate
System model
I SISO system with symbol period Ts and thus symbol rate
Rs = 1/Ts
I We assume ideal Nyquist pulses so the bandwidth is also
W = 1/Ts
I We assume a flat fading channel in which each channel use
corresponds to one symbol
I The channel power gain is g [n] = |h[n]|2 , with pdf p(g )
(exponential for a Rayleigh channel)
I The noise is AWGN with psd N0 /2
I The average transmitted power is P, and hence the
instantaneous SNR is
Pg [n]
γ[n] =
N0 W
Channel Est.
gˆ [n] or γˆ[n] gˆ [n] or γˆ[n]
I BPSK p
Pb = Ps = Q 2γ
I QPSK
√
Ps = 2Q ( γ)
I MPSK p
Ps = 2Q 2γ sin(π/M)
I MPAM r !
2(M − 1) 6γ
Ps = Q 2
M M −1
I MQAM r !
3γ
Ps = 4Q
M −1
A useful approximation for the BER for MQAM modulations is
Pb ≤ 0.2e −1.5γ/(M−1) ,
Rate adaptation
Example
Example
P1 = Pmax P1 , γ 1 ≤ γ < γ 2
γ1
0, 0 ≤ γ < γ 1
0
Example
Adaptive coding
I In adaptive coding, different channel codes,C (γ), are used to
provide different amounts of channel protection against errors
to the transmitted bits
I Intuition: stronger error protection should be provided when γ
is small, whereas a weaker coder should be used when γ is
large
I Adaptive coding is typically achieved by puncturing: not
transmitting certain coded bits in convolutional encoders
Hybrid techniques
I Hybrid techniques can adapt multiple parameters of the
transmission scheme: rate, coding scheme, power, and even
the target BER
I Typical examples include
I Rate and power adaptation
I Adaptive modulation and coding (MCS)