2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Fundamentals of Wireless Communication David Tse 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath 1. Introduction 3 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Course Objective • Past decade has seen a surge of research activities in the field of wireless communication. • Emerging from this research thrust are new points of view on how to communicate effectively over wireless channels. • The goal of this course is to study in a unified way the fundamentals as well as the new research developments. • The concepts are illustrated using examples from several modern wireless systems (GSM, IS-95, CDMA 2000 1x EV-DO, Flarion's Flash OFDM, ArrayComm systems.) 4 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath System Implementation Capacity limits and communication techniques Channel modelling 5 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Course Outline Part I: Basics 2. The Wireless Channel 3. Diversity 4. Multiple Access and Interference Management 5. Capacity of Wireless Channels 6 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Course Outline (2) Part II: Modern Wireless Communication 6. Opportunistic Communication and Multiuser Diversity 7. MIMO I: Spatial Multiplexing and Channel Modeling 8. MIMO II: Capacity and Multiplexing Architectures 9. MIMO III: Diversity-Multiplexing Tradeoff 7 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Assumed background: • Basic signals and systems, linear algebra and proabability. • Basic digital communications. 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath 2. The Wireless Channel 10 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Wireless Mulipath Channel Channel varies at two spatial scales: large scale fading small scale fading 11 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Large-scale fading • In free space, received power attenuates like 1/r 2 . • With reflections and obstructions, can attenuate even more rapidly with distance. Detailed modelling complicated. • Time constants associated with variations are very long as the mobile moves, many seconds or minutes. • More important for cell site planning, less for communication system design. [...]... frequency selective Fundamentals of Wireless Communication, Tse&Viswanath 20 2: The Wireless Channel Effective channel depends on both physical environment and bandwidth! Fundamentals of Wireless Communication, Tse&Viswanath 21 2: The Wireless Channel Time Variations Doppler shift of the i th path Doppler spread Coherence time Fundamentals of Wireless Communication, Tse&Viswanath 22 2: The Wireless Channel... 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath 25 2: The Wireless Channel Types of Channels Fundamentals of Wireless Communication, Tse&Viswanath 26 2: The Wireless Channel Typical Channels are Underspread • Coherence time Tc depends on carrier frequency and vehicular speed, of the order of milliseconds or more • Delay spread Td depends on distance to scatterers, of the... path has Doppler shift of -50 Hz reflected path has shift of +50 Hz Doppler spread = 100 Hz Fundamentals of Wireless Communication, Tse&Viswanath 23 2: The Wireless Channel Doppler Spread Doppler spread is proportional to: • the carrier frequency fc; • the angular spread of arriving paths where θi is the angle the direction of motion makes with the i th path Fundamentals of Wireless Communication, Tse&Viswanath... variation of the order of 100 Hz • Primary driver behind wireless communication system design Fundamentals of Wireless Communication, Tse&Viswanath 12 2: The Wireless Channel Game plan • We wish to understand how physical parameters such as – – – – – carrier frequency mobile speed bandwidth delay spread angular spread impact how a wireless channel behaves from the communication system point of view •... evaluation Fundamentals of Wireless Communication, Tse&Viswanath 13 2: The Wireless Channel Physical Models • Wireless channels can be modeled as linear timevarying systems: where ai(t) and τi(t) are the gain and delay of path i • The time-varying impulse response is: • Consider first the special case when the channel is timeinvariant: Fundamentals of Wireless Communication, Tse&Viswanath 14 2: The Wireless. .. Conversion • Communication takes place at • Processing takes place at baseband Fundamentals of Wireless Communication, Tse&Viswanath 15 2: The Wireless Channel Complex Baseband Equivalent Channel • The frequency response of the system is shifted from the passband to the baseband • Each path is associated with a delay and a complex gain Fundamentals of Wireless Communication, Tse&Viswanath 16 2: The Wireless. .. exponentially distributed • Rician model: 1 line -of- sight plus scattered paths Fundamentals of Wireless Communication, Tse&Viswanath 28 2: The Wireless Channel Correlation over Time • Specified by autocorrelation function and power spectral density of fading process • Example: Clarke’s (or Jake’s) model Fundamentals of Wireless Communication, Tse&Viswanath 29 2: The Wireless Channel Additive Gaussian Noise... Modulation and Sampling Fundamentals of Wireless Communication, Tse&Viswanath 17 2: The Wireless Channel Multipath Resolution Sampled baseband-equivalent channel model: where hl is the l th complex channel tap and the sum is over all paths that fall in the delay bin System resolves the multipaths up to delays of 1/W Fundamentals of Wireless Communication, Tse&Viswanath 18 2: The Wireless Channel Sampling... fading: • Will use this throughout the course Fundamentals of Wireless Communication, Tse&Viswanath 30 2: The Wireless Channel Summary • We have understood how time and frequency selectivity of wireless channels depend on key physical parameters • We have come up with statistical channel models that are useful for analysis and design Fundamentals of Wireless Communication, Tse&Viswanath 31 ... Interpretation • hl is the l th sample of the low-pass version of the channel response hb(¢) • Contribution of the i th path is sinc(W(τ-τi)) sampled at τ=l/W • Contribution is significant only when τi is close to l/W Fundamentals of Wireless Communication, Tse&Viswanath 19 2: The Wireless Channel Flat and Frequency-Selective Fading • Fading occurs when there is destructive interference of the multipaths that contribute . 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Fundamentals of Wireless Communication David Tse 2: The Wireless Channel Fundamentals of Wireless Communication, . The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath 2. The Wireless Channel 10 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Wireless. Capacity of Wireless Channels 6 2: The Wireless Channel Fundamentals of Wireless Communication, Tse&Viswanath Course Outline (2) Part II: Modern Wireless Communication 6. Opportunistic Communication