1. What is Significance of Eb/No? On what factors it is dependent? who provides Eb/No? What is typical Eb/No for AMR 12.2 for Node B and MS?
Answer - Eb_No is related to QOS of a service which in terms related to bit error rate. Technically it is the minimum signal to noise needed by infrastructure equipment after despreading it signal. This is a value used to compare different infrastructure vendors. Eb_No changes with the service type. Typically Eb_No for AMR 12.2 is ~ 4 db for node B and 8 dB for MS. It is infrastructure vendor (NSN) provides the Eb_No for Node B.
The Eb/N0 value is the value that needs to be reached for insuring the targeted service quality. This is the ratio between the energy per bit for the related service over the noise spectral efficiency over the whole spreading band.
The spread signal is characterized by the ratio of the energy per chip over the spectral noise density Ec/N0.
2. What effect is there on signal by spreading and dispreading?
Answer - Spreading will increase the bandwidth of a as signal. A signal of 10 Kb/s will become 40 Kb/s after spreading and will become 10 Kb/s after despreading.
The processing gain term expresses the gain achieved by spreading a narrow band signal over a wideband spectrum.
This gain is the ratio between the spreading chip rate and the actual service bit rate measured at the RLC level
3. Define Processing Gain.
Answer - Processing Gain is ratio between rate of spreaded signal and rate of non spreaded signal.
PG= 10 log (Chip rate /Bit rate)
4. What is a chip rate of WCDMA System? How much is the bandwidth required for WCDMA?
Answer: - 3840 Kc/s. FDD 5 MHZ of paired band. TDD 5 MHz only.
5. What is the processing gain for 384 Kb/s service?
Answer:- =10*Log(3840/384)
=10*log (10)
=10*1
=10
6. What is the relationship of SF and data rate?
Answer; - They are inversely proportional. Lower the SF higher the data rate.
7. What is the relationship between SF and power required?
Answer - The lower the SF, the more power required.
8. What is the relationship with SF and coverage area of different services?
Answer: - They are directly proportional. Lower SF will have less coverage area.
For example Coverage area decreases with increased throughput. If we compare 12.2 Kb/s and 384 Kb/s coverage area.12.2 kb/s coverage area will be bigger then 384 Kb/s coverage area.
9. What is the family of codes used for Chanelization in WCDMA
Answer: - Orthogonal Variable Spreading Factor.(OVSF)
10. What is the minimum and maximum SF in Downlink and uplink for FDD Mode?
Answer; - Minimum of 4 and maximum of 512 chips in downlink
Minimum of 4 and maximum of 256 chips in uplink
11. What is the usage of Channelization code in downlink and uplink?
Answer;- Uplink separation of physical data (DPDCH) and control channel (DPCCH) from same terminal.
Downlink separation of downlink connections to different users within one cell.
12. What is the Chanelization code used for PCPICH (PILOT CHANNEL)?
Answer: - C ch(256,0)
13. What is a typical CPICH power?
Answer - CPICH power typically takes about 8~10% of the total NodeB power. For a 20W (43dBm) NodeB, CPICH is around 2W (35.1 ~ 33dBm).
In urban areas where in-building coverage is taken care of by in-building installations, the CPICH may sometimes go as low as 5% because:
1) The coverage area is small since users are close to the site, and
2) More power can be allocated to traffic channels.
14. How much power usually a NodeB is allocated to control channels?
Answer - The power allocated to control channels may depend on equipment vendor recommendation. Typically no more than 20% of the total NodeB power is allocated to control channels, including CPICH. However, if HSDPA is deployed on the same carrier then the total power allocated to control channel may go up to 25 to 30% because of the additional HSDPA control channels required.
15. What is the usage of scrambling code in WCDMA for both downlink and uplink?
Answer; - There is only one frequency in Downlink. SC is used to separate cells. In uplink it is used to differentiate terminals.
16. How many numbers of SC codes available in Downlink and Uplink?
Answer; - Downlink 512, Uplink several millions.
17. What is the Modulation scheme is used in UMTS for voice service in Downlink and uplink?
Answer; - QPSK in downlink and HPSK (Hybrid Phase shift keying) in uplink.
18. How many slots are there in a WCDMA Frame? How big is a frame in ms. how many chips are there in a slot?
Answer: - WCDMA Frame is 15 slots wide. It is 10ms in length. There are 2560 chips in one slot.
Chip rate is 3840 Kc/s
Length of frame = 10 ms
Number of chips in a frame = 3840 *10=38400 chips
Number of chips in a slot = 38400/15= 2560 chips.
19. Give a simple definition of pole capacity?
Answer - The pole capacity is the theoretical maximum capacity of the system. In WCDMA, this capacity is only theoretical since, once reached, the system goes in an instable state that leads to its collapse. However it is still a reference for expressing the load.
The uplink noise increases with the loading exponentially. When the uplink noise approaches infinity then no more users can be added to a cell – and the cell loading is close to 100% and has reached its “pole capacity”.
Mathematically, to calculate the uplink pole capacity we need to know:
W: chip rate (for UMTS 3,840,000 chips per second)
R: user data rate (assuming 12,200 kbps for CS-12.2k)
f: other-cell to in-cell interference ratio (assuming 65%)
EbNo: Eb/No requirement (assuming 5dB)
AF: Activity factor (assuming 50%)
Pole Capacity = (W/R) / ((1+f) * AF * 10^(EbNo/10)) = 120.6
To calculate the downlink pole capacity we also need to know:
α: downlink channels orthogonality factor (assuming 55%)
Pole Capacity = (W/R) / ((1- α +f) * 10^(EbNo/10)) = 64.06
20. What is typical pole capacity for CS-12.2, PS-64, PS-128 and PS-384?
Answer - With same assumptions as above:
CS-12.2k: 120.6 (UL), 64.1 (DL).
PS-64k: 34.8 (UL), 12.8(DL).
PS-128k: 16.2 (UL), 8.4 (DL).
PS-384k: 16.2 (UL), 2.8 (DL).
PS-384k has only 128k on the uplink, therefore the uplink capacity is the same for both.
21. Different Idle mode tasks UE performs
Answer -In Idle mode, the UE has no connection to the radio network
Keeping UEs in Idle mode minimizes the use of resources both for the UEs and in the network. However, the UEs must still be able to access the system and be reached by the system with acceptable delays. For this, the following procedures need to be performed:
§ PLMN selection and reselection
§ Cell selection and reselection
§ Location Area (LA) and Routing Area (RA) updating
§ Paging
§ System information broadcast
No comments:
Post a Comment