Beach Example 1

Question 1

Types of Spreading Sequences used in CDMA syst.

Answer 1

Max Length Pseudo Random Binary Sequence

Question 2

What are Gold Codes? (2)

Answer 2

• Pairs of preferred m-sequences w/ controlled cross correlation responses.
• Multiple gold codes can be formed from a pair of m-sequences selected by Gold’s Algorithm

Question 3

Frequency Reuse Eff. Definition

Answer 3

in a single freq re-use CDMA network, the adj. cells add to the level of M.I in the network reducing the overall spectrum eff.

Question 4

Rake Reception Definition

Answer 4

mutliple co-phased despreading circuits are employed @ Rx to coherently combine the multiple copies of the wanted wideband transmission appearing @ Rx’s antenna due to multipath propagation

Question 5

Relationship between spreading b/w + # resolvable multipath components

Answer 5

greater the spreading b/w, more multipath components can be resolved

Question 6

Relationship between capacity enhancement, # Rake branches and type of channel characteristic

Answer 6

• Capacity enhancement incr. w/ # Rake branches
  
  • provided that multipath energy w/ sufficient SNR can be resolved within each time bin

Question 7

Fading characteristics of a Rake receiver branch as the spreading b/w is incr. (3)

Answer 7

• Greater the temporal resolution, the more stable the fading becomes (branch by branch basis)
• Less fading requires a lower E_b/N₀ for a given BER
• # users inversely proportional to E_b/N₀

Question 8

Difference between Spreading + Scrambling in the W-CDMA component of UTMS (2)

Answer 8

Spreading - code is applied to all users to expand the b/w

Scrambling - code is unique to each user and applied before transmission

Question 9

How are multi-users accomodated in UTMS DL?

Answer 9

Orthogonal variable spreading factor (OVSF) used to accomodate multi-rate users

• • truly orthogonal, no M.I (cross-correlation) between codes*
• Codes from different branches in the tree can be used to provide different data rates*