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TLT-5606 Spread Spectrum Techniques – Wrap-Up of Part I

TLT-5606 Spread Spectrum Techniques – Wrap-Up of Part I. Toni Huovinen. Introduction and Fundamentals. Spread spectrum (SS) system occupies much wider frequency band than minimum necessary for transmitting the data with given rate. What are benefits from this?

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TLT-5606 Spread Spectrum Techniques – Wrap-Up of Part I

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  1. TLT-5606 Spread Spectrum Techniques – Wrap-Up of Part I Toni Huovinen

  2. Introduction and Fundamentals • Spread spectrum (SS) system occupies much wider frequency band than minimum necessary for transmitting the data with given rate. What are benefits from this? • What is the main compensation mechanism of the inherent loss of spectral efficiency (bits / sec / Hz), e.g., in commercial system based on SS?

  3. Introduction and Fundamentals (Cont’d) • How do you define processing gain (or spreading gain or spreading factor) of the spread spectrum system? • Mention different types of spread spectrum and explain briefly how they work.

  4. Pseudorandom Sequences • What is the difference between synchronous and asynchronous CDMA data models? • Why it is not enough to consider only one symbol duration at time in asynchronous CDMA model? • How do you measure similarity between two spreading codes?

  5. Pseudorandom Sequences (Cont’d) • Use of linear feedback shift register (LFSR) is a practical way to generate chip sequences for spreading codes. Recap how LFSR works. • What is characteristic polynomial of LFSR? • How can you find an output of given LFSR? • How an eavesdropper can determine a used LFSR?

  6. Pseudorandom Sequences (Cont’d) • Why autocorrelation and cross correlation functions are mentioned in context of spreading codes? • What are m-sequences and why they are important? • What are preferred pairs and why they are important? • What are Gold codes and why they are important?

  7. Code Acquisition and Tracking • What means code acquisition? • What means code tracking? • Why they are needed in CDMA systems?

  8. Code Acquisition and Tracking (Cont’d) • Describe briefly how the code acquisition works? • What are the main acquisition strategies? • What means multi-dwell search?

  9. Single-User Detection • What is the best (=minimum bit error probability) linear detector in single user AWGN channel? • What is the best detector among all detectors (including also non-linear detectors) in single user AWGN channel? • What is single user bound and why it is important in CDMA performance analysis?

  10. Single-User Detection (Cont’d) • Is it possible to use MF detector in multi user channel? • What is near–far problem? • How one can compensate a performance loss due to fading in SS system? • What is RAKE receiver and how it works?

  11. Multi-User Detection • What means multi-user detection (MUD) and why it is needed? • We have learnt that a performance of jointly optimum MUD is extremely close to best possible (individually optimum MUD). Why sub-optimum MU receivers, whose performance is worse, are used in practice? • What means asymptotic multi user efficiency? How it looks like for jointly optimum MUD in case of two synchronous users and why?

  12. Multi-User Detection (Cont’d) • How do you define near-far resistance? • What are the sub-optimum MU receivers described in the lectures? Explain briefly how they works? • What means blind MUD?

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