移动通信课件英文版chapter 6.ppt

Chapter 6 Diversity, Capacity and Space- Division Multiple Access 6.1 Introduction Diversity Frequency diversity Time (signal-repetition) diversity Space diversity Receive diversity Transmit diversity Diversity on both transmit and receive Multiple-input, multiple-output (MIMO) User terminal of limited battery power Channel of limited RF bandwidth 6.2 “Space Diversity on Receive” Techniques 6.2.1 Selection Combining 6.2.2 Maximal-Ratio Combining 6.2.3 Equal-Gain Combining 6.2.4 Square-Law Combining 6.2.1 Selection Combining 6.2.1 Selection Combining Given Nr receiver outputs produced by common transmitted signal, logic circuit selects particular receiver output with largest signal-to-noise ratio as received signal. Assumption Frequency-flat: all frequency components constituting the transmitted signal are characterized by same random attenuation and phase shift. Slow-fading: fading remains unchanged during transmission Fading phenomenon is described by Rayleigh distribution. 6.2.1 Selecting Combining Complex envelope of received signal of kth diversity branch is With fading assumed to be slowly varying relative to symbol duration T, we simply the above Eq. to The average signal-to-noise ratio at kth receiver output As mean-square value of is the same for all k , we have 6.2.1 Selecting Combining Instantaneous signal-to-noise ratio Assume average signal-to-noise ratio over short-term fading is same, the probability density functions of random variablesΓk pertaining to induvudal branches as For some signal-to-noise ratio, the associated cumulative distributions of individual branches are 6.2.1 Selecting Combining Probability that all the diversity branches have a signal-to-noise ratio less than threshold γis Cumulative distribution function of random variableΓsc Cumulative distribution function of selection combiner 6.2.1 Selecting Combining Probability density function of For convenience of graphical presentation, we use the scaled probabi