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Step 1: Identify cell with low DL (downlink) throughput
a) The first thing is to identify those cells with low throughput. This thresholdis defined by your network policies and practices (it also depends on your
design parameters). Reports should be run for a significant number of daysso that data is statistically valid.
Step 2: Identify Downlink interference
a) Cells with downlink interference are those whose CQI values are low (anexception to this rule is when most traffic is at the cell edge –bad celllocation-). Analyze the CQI values reported by the UE for
Transmit Diversity MIMO one layer
MIMO two layers
Typical values for transmit diversity oscillate between 7 and 8.
Typical values for MIMO one and two layers oscillate between 10 and 12.
b) If low CQI values are found after a CQI report is obtained, then downlinkinterference might be the cause of low throughput.
c) Common sources of interference in the 700 MHz band (LTE deployment inthe USA) are: inter-modulation interference, cell jammers and wirelessmicrophones
• The isolation between cells which are assigned the same physical layer cell
identity should be maximised and should be sufficiently great to ensure that UE
never simultaneously receive the same identity from more than a single cell• Whenever possible, cells belonging to the same eNodeB should be allocated iden-
tities from within the same group
• Specific physical layer cell identities should be excluded from the plan to allow for
future network expansion
• There should be some level of co-ordination across international borders when
allocating physical layer cell identities• Better to avoid Cell IDs with identical values mod 3 among neighbors to distinguish
The Received Signal Strength Indicator (RSSI) in the uplink is affected by the parameter settingsthat govern open loop power control in LTE. Open loop power control is used during Random
Access.
The random access is often the first transmission from the UE, and it is a short transmission
(less than 3 ms at most). Consequently, the network does not have an opportunity to power
control the PRACH transmitted by the UE. Instead, the UE must estimate the minimum amount
of power it needs to send the access request without causing excessive interference.The UE receives a number of key parameters for PRACH power control in SIB 2, including:
Preamble Initial Received Target Power: The power level the eNB would like to receive for a
random access. The default value is -104 dBm.
Power Ramping Step: The amount of additional power to be used every time the random
access is attempted again. This can be 0, 2, 4 or 6 dB.
Preamble Trans Max: The maximum number of times a random access can be attemptedbefore the UE gives up, to a maximum of 10 tries.
RA Response Window Size: The number of subframes the UE will wait for a response after a
random access, between two and 10 subframes.
T300: the time the UE has to receive the RRC connection Setup message from the eNodeB.
The UE will determine the initial power level based on the Preamble Initial Received Target
Power value and an estimate of the uplink Path Loss (PL) as follows:
Pinitial = min (Pmax, Preamble Initial Received Target Power + PL); where Pmax is the
maximum transmit power of the UE, based on its category.
If the eNB fails to respond to the random access in the designated time window (RA
Response Window Size), then it can repeat the random access (after waiting at least four
more subframes), increasing its power level by the Power Ramping Step value. If no
response is received after Preamble Trans Max attempts, then the UE will return an
access failed indication.
The values of Preamble Initial Target Power and Power Ramping Step directly affect RSSI.
High values of both parameters may result in high RSSI, particularly in indoor
environments (i.e.: Airports, convention centers, etc.) and events (i.e.: foot ball games atstadiums, concerts, etc.). In this type of environments, a high concentration of UEs exists
and often times, many of them try accessing the network at the same time. Even when a
different UE has selected a different preamble and has calculated the right amount of
power, the eNodeB often times will only answer to ONE of them (this is vendor
implementation dependent) per sub-frame, leading to the rest of the UE to increase their
transmit power. If this condition prevails, quickly, all UEs will be transmitting at ismaximum transmit power in less than a second, producing a high RSSI at the eNodeB.
Values of -110 to -112 dBm are recommended for Preamble Initial Target Power and 2dB
for Power Ramping step for events and indoor environments. For outdoor environments,
depending on the load and RSSI, values of -104 dBm and 4dB could be used, respectively.
Energy by Allocating ResourcesPhysical Resource Block (PRB) allocation effects on LTE UE transmission power and energy
consumption were examined. The simulation results, based on a mapping from transmissionpower to energy consumption, show that it is more energy efficient to allocate as many PRBs as
possible to a single user instead of assigning several users less PRBs. On average at least 24 %
energy can be saved if a user is allocated an entire 10 MHz channel (48 PRBs) instead of 8 PRBs.
LTE’s Uplink Power Control entails that users with more PRBs will transmit with higher power,
but the throughput increases concurrently and therefore energy can be saved. Further more the
applied power consumption model entails that the UE’s efficiency increases when the transmit
power increases. An equal opportunity turn-based PRB scheduler was implemented to evaluatehow scheduling of maximum 6, 8, and 10simultaneous users affect the energy consumption. The
results show scheduling maximum 10 users instead of 6 increases the average transmission
time with∼4 % and the average energy consumption with ∼6 %. Yet there is no incentive to
allow more than 6 users because the cell throughput is independent of the number of users. The
conclusion is that one user should be allocated as many PRBs as possible, while limiting the
number of simultaneous users to reduce the average waiting time.
The Flexi Multiradio BTS supports with this feature an extended range of
3GPP settings for the long DRX cycle, two additional operator configurable DRXprofiles, and uplink Out-of-Sync handling.
Benefits
The extension to support longer settings for the long DRX cycle leads to a lower UE
power consumption mainly for UEs with only occasional data transmission.
Requirements
Software requirementsTable 37 Software requirements lists the software required for this feature.
Hardware requirements
This feature requires no new or additional hardware.
Functional description
Feature scope
Extended DRX settings feature improves power savings for the UE by supportingalso settings of the long DRX cycle beyond 80ms from the 3GPP defined range. Those
additional savings in power are feasible for bursty traffic patterns (i.e. short phases
with data transmission followed by long phases of idle period). The potential
additional power savings come, however, at the cost of increased latency for DL
transmission whenever the UE is in DRX sleep mode.
LTE473 is an extension to feature LTE 42:Support of DRX in RRC Connected. LTE473: Extended DRX settings feature
comprises three subfeatures:
support of an extended value range of the long DRX Cycle
two additional operator configurable DRX profiles
uplink Out-of-Sync handlingSupport of an extended value range of the long DRX Cycle
Two profiles which support extended 3GPP value range for the long DRX cycle (160, 320ms in Profile4; 640, 1280, 2560ms in Profile5).
Two additional operator configurable DRX profiles
Two additional operator configurable DRX profiles are introduced with this feature in order to allow more flexible definition of different
DRX use cases, e.g. Out-of-Sync handling.
drxProfile4: “non-GBR” (<500ms, e.g. QCI 5)
The profile is optimized for non-GBR bearers with specific latency requirements that allow setting medium DRX cycle length (e.g. IMS
signaling)
drxProfile5: “non-GBR” (>=500ms)
The profile is appropriate for non-GBR bearers without specific latency requirements that allow setting long DRX cycle length (e.g. webbrowsing)
Additional profiles will only yield some gains if gaps in UE data transmission are sufficiently large (e.g., always-on devices doing only an
occasional data transmission with gaps of at least several tens of seconds). The UEs are kept DRX Active always during phases of data
transmission and dropped to UL out-of-sync afterwards (the UE benefits from the extended DRX when in UL Out-of-Sync state).
Any kind of traffic mapped to QCIs using such profiles should be latency tolerant as to match at least the long DRX cycle setting. Extended
DRX is supported for QCI 5-9 (i.e., QCI types without any delay guarantees).
Uplink Out-of-Sync handling
The uplink Out-of-Sync handling comprises the following two subfeatures:
Uplink Out-of-Sync enforcement By using very long settings for the DRX cycle, the UE may go to or is even actively sent to the uplink Out-of-Sync status. For this timing
alignment is stopped some time after UE has finished data transmission.
Transition to uplink In-Sync
DL data transmission trigger
The eNodeB initiates a random access procedure for UEs which are in uplink Out-of-Sync and have data for downlink transmission. The
eNodeB provides in this case the RACH parameters via the PDCCH order to the UE.
UL data transmission trigger
During the UL Out-of-Sync state, UE may start a contention based random access procedure in order to transmit data on uplink
Following the transition to In-Sync, UEs are reconfigured with any resources released during UL Out-of-Sync transition (resourceson PUCCH and for SRS, if applicable).