1. What are the RRC
states?
There are 4 RRC
States: Cell_DCH, Cell_FACH, URA_PCH and Cell_PCH.
URA = UTRAN
Registration Area.
VISIT OUR FACEBOOK PAGE
2. What are
transparent mode, acknowledged mode and unacknowledged mode?
· Transparent mode
corresponds to the lowest service of the RLC layer, no controls and no
detection of missing
data.
· Unacknowledged mode
offers the possibility of segment and concatenate of data but no
error correction or
retransmission therefore no guarantee of delivery.
· Acknowledged mode
offers, in addition to UM mode functions, acknowledgement of
transmission, flow
control, error correction and retransmission.
3. Which layer(s)
perform ciphering function?
RRC – for acknowledged
mode (AM) and unacknowledged mode (UM).
MAC – for transparent
mode (TM).
4. What is OVSF?
Orthogonal Variable
Spreading Factor.
VISIT OUR FACEBOOK PAGE
5. How many OVSF code
spaces are available?
· Total OVSF codes =
256.
· Reserved: 1 SF64 for
S-CCPCH, 1 SF256 for CPICH, P-CCPCH, PICH and AICH each.
· Total available code
space = 256 – 4 (1 SF64) – 4 (4 SF256) = 248.
6. Can code space
limit the cell capacity?
Yes, cell capacity can
be hard-limited by code space. Take CS-12.2k for example:
· A CS-12.2k bearer
needs 1 SF128 code.
· Total available
codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.
· Consider
soft-handover factor of 1.8: 124 / 1.8 = 68 uers/cell.
7. Can a user have
OVSF code as “1111”?
No, because “1111…”
(256 times) is used by CPICH.
8. What are the symbol
rates (bits per symbol) for BPSK, QPSK, 8PSK and 16QAM?
· BPSK:
.
· QPSK:
VISIT OUR FACEBOOK PAGE
· 8PSK:
· 16QAM:
9. Briefly describe
UMTS frame structure.
· UMTS frame duration
= 10ms.
· Each frame is
divided into 15 timeslots.
· Each timeslot is
divided into 2560 chips.
· Therefore 2560
chips/TS * 15 TS/frame * (1000ms/10ms) frame/sec = 3,840,000
chip/sec.
VISIT OUR FACEBOOK PAGE
10. What is cell
selection criterion?
Cell selection is
based on:
· Qmean: the average
SIR of the target cell.
· Qmin: minimum
required SIR.
· Pcompensation: a
correction value for difference UE classes.
S = Qmean - Qmin -
Pcompensation
· If S>0 then the
cell is a valid candidate.
· A UE will camp on
the cell with the highest S.
11. Briefly describe
Capacity Management and its functions:
Capacity Management is
responsible for the control of the load in the cell. It consists of 3
main functions:
· Dedicated Monitored
Resource Handling: tracks utilization of critical resources of the
system.
· Admission Control:
accepts/refuses admission requests based on the current load on the
dedicated monitored
resources and the characteristics of the request
· Congestion Control:
detects/resolves overload situations
12. What are the major
4 KPIs in propagation model tuning and typical acceptable values?
The 4 KPIs are
standard deviation error, root mean square error, mean error and correlation
coefficient. The
typical acceptable values are:
· Standard deviation
error: the smaller the better, usually 7 to 9dB.
· Mean error: the
smaller the better, usually 2 to3.
· Root mean square
error: the smaller the better, usually
· Correlation
coefficient: the larger the better, usually 70% to 90%.
13. What is the
minimum number of bins required for a certain propagation model?
The more bins the more
likely to come up with a good model. Usually a minimum of 2,000
bines is considered
acceptable, but sometimes as low as 500 bins may be accepted.
VISIT OUR FACEBOOK PAGE
14. How many
scrambling codes are there?
There are 512
scrambling codes in the downlink and 16,777,216 codes in the uplink.
15. How many
scrambling code groups are there for downlink?
There are 64 code
groups, each group has 8 scrambling codes.
16. Can we assign same
scrambling codes to sister sectors (sectors on same site)?
No, because scrambling
code on the downlink is used for cell identity. As a requirement,
scrambling codes have
to maintain a safe separation to avoid interference.
17. Are scrambling
codes orthogonal?
No, scrambling codes
are not orthogonal since they are not synchronized at each receiver.
They are pseudo random
sequences of codes.
18. Can we assign
scrambling codes 1, 2 and 3 to sister sectors?
Yes.
19. In IS-95 we have a
PN reuse factor (PN step size) and therefore cannot use all 512 PN
codes, why isn’t it
necessary for UMTS scrambling codes?
Because IS-95 is a
synchronized network, different PN codes have the same code sequence
with a time shift,
therefore we need to maintain a certain PN step size to avoid multi-path
problem. For example,
if two sectors in the neighborhood have a small PN separation then
signal arriving from
cell A may run into the time domain of cell B, causing interference.
UMTS, on the other
hand, is not a synchronized network and all scrambling codes are
mutually orthogonal so
no need to maintain a step size.
VISIT OUR FACEBOOK PAGE
20. What are coverage
thresholds in your UMTS design and why?
The coverage
thresholds are based on UE sensitivity, fading and penetration loss. Assuming
UE sensitivity of
-110dBm, fade margin of 5dB:
· Outdoor: -110dBm
sensitivity + 5dB fade margin = -105dBm.
· In-vehicle: -110dBm
+ 5dB + 8dB in-vehicle penetration loss = -97dBm.
· In-building: -110dBm
+ 5dB + 15dB in-building penetration loss = -90dBm.
21. What is the Ec/Io
target in your design?
The Ec/Io target
typically is between -12 to -14dB. However, if a network is designed for
data then the Ec/Io
target could go higher to around -10dB because server dominance is more
critical for a data
network – since there isn’t software in the downlink.
0 comments:
Post a Comment