Thursday, July 26, 2012

UE Measurements

Intra-frequency measurements: measurements on downlink physical channels at the same frequency as the active set. A measurement object corresponds to one cell.
Inter-frequency measurements: measurements on downlink physical channels at frequencies that differ from the frequency of the active set. A measurement object corresponds to one cell.
Inter-RAT measurements: measurements on downlink physical channels belonging to another radio access technology than UTRAN, e.g. GSM. A measurement object corresponds to one cell.
Traffic volume measurements: measurements on uplink traffic volume. A measurement object corresponds to one cell.
Quality measurements: Measurements of downlink quality parameters, e.g. downlink transport block error rate. A measurement object corresponds to one transport channel in case of BLER. A measurement object corresponds to one timeslot in case of SIR (TDD only).
UE-internal measurements: Measurements of UE transmission power and UE received signal level.
UE positioning measurements: Measurements of UE position.The UE supports a number of measurements running in parallel. The UE also supports that each measurement is controlled and reported independently of every other measurement.

Wednesday, July 25, 2012

Cyclic Delay Diversity

Cyclic Delay Diversity (CDD) is a simple approach to introduce spatial diversity to an Orthogonal Frequency Division Multiplexing (OFDM) based transmission scheme that itself has no built-in diversity. It also can be regarded as a Space-Time Code (STC).
But in contrast to that there is no additional effort in the receiver necessary, since the different codewords result in a changed channel impulse response in the receiver. They insert virtual echos and thus increase the frequency selectivity of the channel seen by the receiver. Cyclic Delay Diversity (CDD) is a diversity scheme used in OFDM-based telecommunication systems, transforming spatial diversity into frequency diversity avoiding intersymbol interference.

Tuesday, July 24, 2012

RSRP and RSRQ


In cellular networks, when a mobile moves from cell to cell and performs cell selection/reselection and handover, it has to measure the signal strength/quality of the neighbor cells. In LTE network, a UE measures two parameters on reference signal: RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality).

RSRP is a RSSI type of measurement. It measures the average received power over the resource elements that carry cell-specific reference signals within certain frequency bandwidth. RSRP is applicable in both RRC_idle and RRC_connected modes, while RSRQ is only applicable in RRC_connected mode. In the procedure of cell selection and cell reselection in idle mode, RSRP is used.

RSRQ is a C/I type of measurement and it indicates the quality of the received reference signal. It is defined as (N*RSRP)/(E-UTRA Carrier RSSI), where N makes sure the nominator and denominator are measured over the same frequency bandwidth.

The carrier RSSI (Receive Strength Signal Indicator) measures the average total received power observed only in OFDM symbols containing reference symbols for antenna port 0 (i.e., OFDM symbol 0 & 4 in a slot) in the measurement bandwidth over N resource blocks. The total received power of the carrier RSSI includes the power from co-channel serving & non-serving cells, adjacent channel interference, thermal noise, etc.

The RSRQ measurement provides additional information when RSRP is not sufficient to make a reliable handover or cell reselection decision. In the procedure of handover, the LTE specification provides the flexibility of using RSRP, RSRQ, or both.

Thursday, July 12, 2012

Benefits of CPICH Optimization

Benefits of CPICH Optimization
  • Improving current 3G coverage and increase 3G traffic
  • Improve in-building penetration for 3G
  • Reduce IRAT HO to 2G
  • Offload traffic from 2G layer

Tuesday, July 10, 2012

What is Pilot Polution?

In idle or cell_FACH mode, phenomenon of the pilot pollution is that a UE cannot firmly camp on a cell at one location because of receiving many pilot channels with similar quality (or signal strength), i.e., Ec/No (or RSCP).
The condition to determine the area has pilot pollution in idle or cell_FACH mode is that third pilot appears in the cell re-selection region.
In cell_DCH mode, phenomenon of the pilot pollution is that a UE at one location frequently changes its active set cells (active set update rate is very high) because of receiving many pilot channels with similar quality (or signal strength), i.e., Ec/No (or RSCP). It causes high signaling load in RRC and Iub interfaces and the capacity of RNC is consequently reduced.
Solution for Pilot Polution in the network:
Reason – no dominant cell
The reason is too many overlapping cells at an area due to poor cell planning.
Solution 1
The direct solution is to remove the cells overlapping by changing the antenna configurations or reducing pilot powers of the unwanted cells.
Solution 2
The most effective solution is to increase the pilot channel power Primary CPICH power of the desired cell.
Solution 3
For the pilot pollution in idle or cell_FACH mode, Q Offset 2sn (CPICH Ec/No) parameter of the desired cell can be increased to create a dominated cell.

Sunday, July 8, 2012

Pilot Channel failure - High Downlink Interference

Symptoms:

From the drive test, following symptoms will be observed by using TEMS:
• Received Ec/No of the pilot channel is less than –16dB and
• Received RSCP of the pilot channel is high enough to maintain the connection,e.g. >-   100dBm and
• DL RSSI is very high and
• The connection finally drops.

Good Excel Sheet on CPICH Calculator

Wednesday, July 4, 2012

What are the functionality of eNodeB?

E-UTRAN consists solely of the evolved Node B (eNB), which is responsible for all radio interface functionality.
eNB is the RAN node in the EPS architecture that is responsible for radio transmission to and reception from UEs in one or more cells.
The eNB is connected to EPC nodes by means of an S1 interface.The eNB is also connected to its neighbor eNBs by means of the
X2 interface. Some significant changes have been made to the eNB functional allocation compared to UTRAN. Most Rel-6 RNC
functionality has been moved to the E-UTRAN eNB. Below follows a description of the functionality provided by eNB.

Good PDF Document on LTE Functionality