Podcast
Questions and Answers
In wireless communication, what are the two spatial scales at which the wireless channel varies?
In wireless communication, what are the two spatial scales at which the wireless channel varies?
- Large scale fading and small scale fading (correct)
- Primary fading and secondary fading
- Global fading and local fading
- Macroscopic fading and microscopic fading
What is the time constant associated with variations in large-scale fading as the mobile moves?
What is the time constant associated with variations in large-scale fading as the mobile moves?
- Many seconds or minutes (correct)
- Milliseconds
- Nanoseconds
- Hours
In free space, how does received power attenuate?
In free space, how does received power attenuate?
- Exponentially
- Like $1/r^2$ (correct)
- Linearly
- Like $r^2$
Which term is used to describe the attenuation of received power with reflections and obstructions?
Which term is used to describe the attenuation of received power with reflections and obstructions?
What is the goal of the course mentioned in the text?
What is the goal of the course mentioned in the text?
Which day of the course is dedicated to studying MIMO?
Which day of the course is dedicated to studying MIMO?
What is the focus of Day 3 of the course?
What is the focus of Day 3 of the course?
Which concept is illustrated using examples from several modern wireless systems such as GSM, IS-95, and CDMA 2000 1x EV-DO?
Which concept is illustrated using examples from several modern wireless systems such as GSM, IS-95, and CDMA 2000 1x EV-DO?
What is the term used to describe the comparison of 3 systems in the context of multiple access and interference management?
What is the term used to describe the comparison of 3 systems in the context of multiple access and interference management?
What is the primary focus of the course outlined in the text?
What is the primary focus of the course outlined in the text?
Which type of channel has a capacity close to that of the AWGN channel when only receiver CSI is available?
Which type of channel has a capacity close to that of the AWGN channel when only receiver CSI is available?
What is needed to address the unreliability and poor outage capacity in a slow fading channel?
What is needed to address the unreliability and poor outage capacity in a slow fading channel?
In which domain is waterfilling used for addressing the challenges in a slow fading channel?
In which domain is waterfilling used for addressing the challenges in a slow fading channel?
What can have a capacity greater than that of the AWGN channel when full CSI is available in a fast fading channel?
What can have a capacity greater than that of the AWGN channel when full CSI is available in a fast fading channel?
What type of channel provides more opportunities for performance boost when full CSI is available?
What type of channel provides more opportunities for performance boost when full CSI is available?
In which regime does waterfilling in frequency domain occur?
In which regime does waterfilling in frequency domain occur?
What is a source of unreliability and very poor outage capacity?
What is a source of unreliability and very poor outage capacity?
What is powerful in multiuser situations, providing more opportunities for performance boost?
What is powerful in multiuser situations, providing more opportunities for performance boost?
What type of diversity is mentioned as a solution to address the unreliability in a slow fading channel?
What type of diversity is mentioned as a solution to address the unreliability in a slow fading channel?
What incurs only a small penalty in capacity when present in a fast fading channel with only receiver CSI?
What incurs only a small penalty in capacity when present in a fast fading channel with only receiver CSI?
What is the primary driver behind wireless communication system design?
What is the primary driver behind wireless communication system design?
What is the frequency response of the system shifted from the passband to the baseband for?
What is the frequency response of the system shifted from the passband to the baseband for?
What allows the system to resolve multipaths up to delays of 1/W?
What allows the system to resolve multipaths up to delays of 1/W?
What is crucial for increasing reliability in communication over flat fading channels?
What is crucial for increasing reliability in communication over flat fading channels?
What is used to increase diversity and improve reliability in wireless communication?
What is used to increase diversity and improve reliability in wireless communication?
What provides a fundamental characterization of coded performance in wireless communication?
What provides a fundamental characterization of coded performance in wireless communication?
Which method is used to obtain time diversity?
Which method is used to obtain time diversity?
What is crucial for exploiting added diversity efficiently?
What is crucial for exploiting added diversity efficiently?
What is used to enhance wireless communication performance?
What is used to enhance wireless communication performance?
What are ai(t) and $\tau_i(t)$ used to represent in wireless channel modeling?
What are ai(t) and $\tau_i(t)$ used to represent in wireless channel modeling?
What is the primary driver behind wireless communication system design?
What is the primary driver behind wireless communication system design?
What is the frequency response of the system shifted from the passband to the baseband in wireless communication?
What is the frequency response of the system shifted from the passband to the baseband in wireless communication?
What is the limit for resolving multipaths by sampling the baseband-equivalent channel model?
What is the limit for resolving multipaths by sampling the baseband-equivalent channel model?
Which statistical models are based on the statistical ensemble of channels in wireless communication?
Which statistical models are based on the statistical ensemble of channels in wireless communication?
Which method is crucial for increasing reliability in communication over flat fading channels?
Which method is crucial for increasing reliability in communication over flat fading channels?
How can time diversity be obtained in wireless communication?
How can time diversity be obtained in wireless communication?
Which method is used to increase diversity and improve reliability in wireless communication?
Which method is used to increase diversity and improve reliability in wireless communication?
Which approaches are used to enhance wireless communication performance in frequency diversity?
Which approaches are used to enhance wireless communication performance in frequency diversity?
What provides a fundamental characterization of coded performance in wireless communication?
What provides a fundamental characterization of coded performance in wireless communication?
What is the representation for the gain and delay of path i in wireless channels?
What is the representation for the gain and delay of path i in wireless channels?
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Study Notes
Wireless Communication: Understanding Multipath Fading and Diversity
- Wireless communication occurs at high carrier frequencies, leading to multipath fading due to constructive and destructive interference of transmitted waves.
- Channel variation occurs when a mobile moves a distance of the order of the carrier wavelength, which translates to channel variation of the order of 100 Hz for vehicular speeds.
- The primary driver behind wireless communication system design is to understand how physical parameters such as carrier frequency, mobile speed, bandwidth, and delay spread impact wireless channel behavior.
- Wireless channels can be modeled as linear time-varying systems, with ai(t) and i(t) representing the gain and delay of path i.
- Communication takes place at passband [f_c-W/2, f_c+ W/2], and processing at baseband [-W/2,W/2], with the frequency response of the system shifted from the passband to the baseband.
- Sampling the baseband-equivalent channel model allows the system to resolve multipaths up to delays of 1/W, with fading occurring due to destructive interference of the multipaths contributing to a tap.
- Statistical models based on the statistical ensemble of channels, such as Rayleigh flat fading and Rician models, are used for design and performance analysis.
- Diversity is crucial for increasing reliability in communication over flat fading channels, with time, frequency, and space diversity being key methods for exploiting added diversity efficiently.
- Time diversity can be obtained by interleaving and coding over symbols across different coherent time periods, with the amount of diversity limited by delay constraints and channel variation speed.
- Antenna diversity, space-time codes, and cooperative diversity are methods used to increase diversity and improve reliability in wireless communication.
- Frequency diversity approaches such as time-domain equalization, direct-sequence spread spectrum, and orthogonal frequency-division multiplexing (OFDM) are used to enhance wireless communication performance.
- Information theory provides a fundamental characterization of coded performance in wireless communication, identifying the impact of channel resources and suggesting new communication methods.
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