tlt-5606 spread spectrum techniques – wrap-up of part i

19.04.23Oma nimi ja esityksen aihe vaihdettava mastersivulla

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?

• What is the main compensation mechanism of the inherent loss of spectral efficiency (bits / sec / Hz), e.g., in commercial system based on SS?


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.


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?


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?


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?


Code Acquisition and Tracking

• What means code acquisition?

• What means code tracking?

• Why they are needed in CDMA systems?


Code Acquisition and Tracking (Cont’d)

• Describe briefly how the code acquisition works?

• What are the main acquisition strategies?

• What means multi-dwell search?


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?


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?


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?


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?

tlt-5606 spread spectrum techniques – wrap-up of part i

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