Prerequisites

Before You Begin

This chapter builds on linear algebra (Chapter 1), probability theory (Chapter 2), wireless channel modelling (Chapter 6), digital modulation (Chapter 8), and detection/estimation in fading (Chapter 9). Diversity techniques exploit independent fading across space, time, or frequency to combat the severe performance degradation caused by deep fades.

  • Vectors, norms, and inner products(Review ch01)

    Self-check: Can you compute the norm βˆ₯hβˆ₯\|\mathbf{h}\| of a complex channel vector h∈CL\mathbf{h} \in \mathbb{C}^L and express βˆ₯hβˆ₯2\|\mathbf{h}\|^2 as βˆ‘l=1L∣hl∣2\sum_{l=1}^{L} |h_l|^2?

  • Random variables, expectation, and independence(Review ch02)

    Self-check: Can you compute E[βˆ‘l=1LXl]E[\sum_{l=1}^{L} X_l] when X1,…,XLX_1, \ldots, X_L are independent and identically distributed random variables?

  • Chi-squared and exponential distributions(Review ch02)

    Self-check: Do you know the PDF of a sum of LL independent exponential random variables (Erlang distribution) and its connection to the chi-squared distribution with 2L2L degrees of freedom?

  • Rayleigh and Rician fading models(Review ch06)

    Self-check: Can you state the PDF of the instantaneous SNR Ξ³\gamma for a single Rayleigh fading link and compute P(Ξ³<Ξ³0)P(\gamma < \gamma_0)?

  • Coherence time, coherence bandwidth, and fading correlation(Review ch06)

    Self-check: Can you explain when two channel realisations are approximately independent based on the coherence time TcT_c and coherence bandwidth BcB_c?

  • BER in AWGN and Rayleigh fading(Review ch08)

    Self-check: Can you state the BER for BPSK in AWGN (Pb=Q(2Eb/N0)P_b = Q(\sqrt{2E_b/N_0})) and in Rayleigh fading (Pbβ‰ˆ1/(4Ξ³Λ‰)P_b \approx 1/(4\bar{\gamma}) at high SNR)?

  • Detection and estimation in fading channels(Review ch09)

    Self-check: Can you explain the difference between coherent detection (requires CSI) and non-coherent detection, and state the pairwise error probability in fading?

Chapter 10 Notation

Key symbols introduced or heavily used in this chapter.

SymbolMeaningIntroduced
LLNumber of diversity branchess01
ddDiversity order (d=βˆ’lim⁑SNRβ†’βˆžlog⁑Pe/log⁑SNRd = -\lim_{\text{SNR}\to\infty} \log P_e / \log \text{SNR})s01
Ξ³l\gamma_lInstantaneous SNR on the ll-th diversity branchs01
Ξ³Λ‰\bar{\gamma}Average SNR per branchs01
γSC\gamma_{\text{SC}}Output SNR of selection combining (max⁑lγl\max_l \gamma_l)s02
Ξ³EGC\gamma_{\text{EGC}}Output SNR of equal-gain combinings02
Ξ³MRC\gamma_{\text{MRC}}Output SNR of maximal-ratio combining (βˆ‘lΞ³l\sum_l \gamma_l)s02
hlh_lComplex channel gain on the ll-th branchs02
H\mathbf{H}Space-time channel matrix (Alamouti and STBC context)s03
ΞΌ\muParameter ΞΌ=Ξ³Λ‰/(1+Ξ³Λ‰)\mu = \sqrt{\bar{\gamma}/(1+\bar{\gamma})} in MRC BER expressionss02
TcT_cCoherence time of the channels04
BcB_cCoherence bandwidth of the channels04
NtN_tNumber of transmit antennass03
NrN_rNumber of receive antennass02