TDMA (Time
Division Multiple Access) refers to a digital RF link
where multiple phones share a single carrier frequency by taking turns. Each
phone gets the channel exclusively for a certain time slice, then gives it up
while all the other phones take their turn. TDMA is also used sometimes to
refer specifically to the standard covered by IS-136, which is a source of confusion
because GSM also uses a TDMA air interface, as
does IDEN, and neither of those systems are compatible with IS-136.
Rake receiver
Rake receiver is
the digital section of a CDMA receiver which permits the phone (or cell) to
separate out the relevant signal from all the other signals. The relevant
signal will be encoded with a known Walsh
Code and
a known phase of the Short
code, and the rake receiver can do this because the
Walsh codes are orthogonal and the Short code is orthogonal to
itself at different offsets. The rake receiver is capable of receiving multiple
signal sources and adding them together using multiple fingers, each
of which has the ability to use a separate phase of the short code and long code and a separate Walsh code if
necessary. Different fingers might track multiple signals from the same cell
(arriving at slightly different times due to multipath) or might track separate cells due to soft handoff.
Chips in CDMA
Chip in the context of CDMA is distinct from bit and refers to binary digits transmitted over the RF link. The chip rate in IS-95 is 1.2288 MHz (thus allowing adequate guard bands to permit the carriers to be spaced 1.25 MHz apart). Each bit is represented by many chips, and if a majority of the chips get through then the bit can be reconstructed properly. The number of chips representing each bit varies depending on the bit rate. When using an 8K Vocoder (such as EVRC) there are 128 chips for each bit. Chips as such don't contain data because both the sender and receiver know the spreading pattern used to create them from a bit, and as such are not directly subject to the laws of Information Theory. Though there are many phones simultaneously using a single frequency to transmit full chiprate, that means that the channel is not saturated unless the bitrate approaches the bandwidth of the carrier.
2G HO Algorithm
2G
Handover Optimization
Classification
by Reason
Timing advance (TA) Emergency HO
Triggering condition
_ The actual TA > TA HO Thrsh.
Object cell selection
_ The cell must be of the highest
priority in the candidate cell sequence and
meet the following restrictions.
Restriction
_ The service cell cannot be the
object cell.
_ HO is not allowed when TA Thresh.
of the neighboring cell with the same
BTS
is smaller than that of the service cell.
Bad
Quality HO
Triggering condition
_ UL receiving quality >=UL
receiving quality thrsh. of the service cell.
_ OR DL receiving quality >=DL
receiving quality thrsh. of the service
cell.
Object cell selection
_ The cells must be of the highest
priority in the candidate cell
sequence and meet the following restrictions.
Restriction
_ Handover to the neighboring cell with
the highest priority. If there is no
neighboring cell, handover to the service cell, and the channel at
different TRX is preference.
_ Rx Level (n) > Rx Level (s) +
Inter Cell HO Hysteresis + BQ HO Margin
Signal
Level Rapid Drop HO
Triggering condition
_ Due to downlink signal level drop
_ Triggered upon detecting rapid
level drop during MS busy mode
_ Object cell selection
_ The neighboring cell with the
highest priority and whose priority is higher
than that of the service cell in the candidate cell group.
_ Restriction
_ The service cell cannot be the
object cell.
Interference
HO
Triggering condition
_ UL receiving quality>=Service
cell UL receiving quality Thrsh. AND
UL receiving level>=Service cell UL receiving level Thrsh.
_ OR DL receiving
quality>=Service cell DL receiving quality Thrsh.
AND DL receiving level>=Service cell DL receiving level Thrsh.
Object cell selection
_ The cells must be of the highest
priority in the candidate cell
sequence and meet the following restrictions.
Restriction
_ The service cell that is not in
the penalty time for intra-cell handover.
_ The neighboring cell with the
receiving level higher than the inter
layer
HO Thrsh.
Load
HO
Triggering condition
_ The load HO switch of the service
cell is enabled.
_ The system signaling flow is not
larger than the Load HO system flow Thrsh.
_ The service cell traffic is
larger than the Load HO Thrsh.
_ The DL receiving level is in the
load HO zones.
Object cell selection
_ The service cell cannot be the
object cell.
_ The traffic of the neighboring
cell must be lower than its load HO receiving
thrsh.
_ The neighboring cell with the
receiving level higher than the inter layer HO
Thrsh.
Restriction
_ It is not available with SDCCH.
_ Load HO just occur within the
same BSC.
Edge
HO
Triggering condition
_ The DL receiving level < Edge
HO DL RX_LEV Thrsh.
_ OR The UL receiving level <
Edge HO UL RX_LEV Thrsh.
_ Satisfying P/N rule.
Object cell selection
_ The service cell cannot be the
object cell.
_ The neighboring cell with the
highest priority and whose priority is
higher
than that of the service cell.
Layer
HO
Triggering condition
_ The layer of the object cell is
lower than that of the service cell.
_ The DL level of the object cell
is higher than the inter layer HO thrsh.
_ Satisfying P/N rule.
Object cell selection
_ The service cell cannot be the
object cell.
_ The neighboring cell with the
highest priority and whose priority is
higher
than that of the service cell
PBGT
HO
Triggering condition
_ The layer and level of the object
cell are the same as those of the
service cell.
_ The DL level must be the result
of the following formula.
Object cell selection
_ The service cell cannot be the
object cell.
_ The neighboring cell with the
highest priority and whose priority is
higher than that of the service cell.
Restriction
_ It is not available with SDCCH.
Fast-Moving HO
Triggering condition
_ In Fast Moving Watch Time, the
mobile phone moves through P cells
of N.
_ The layer of N cells must be less
than four (none Umbrella cell).
Object cell selection
_ The neighboring cell with the
highest priority and meet the following
condition.
_ The layer of the object cell must
be no less than four, that is, the
Umbrella cell.
_ The receiving level of the object
cell >= the inter layer HO thrsh. +
inter
layer HO hysterisis.
MIMO ( Multi Inpit Multi Output )
MIMO
Systems can provide two types of gain:
Spatial Multiplexing Gain and transmit Diversity Gain
In
Spatial Multiplexing Gain , maximum transmission rate can be achieved by sending different data streams at different antennas
Whereas in Diversity Gain, maximum quality(QOS) can
be achieved by sending same data streams
to different antennas.
There
is a tradeoff between these two gains as
spatial diversity can be achieved under good radio conditions where as transmit
diversity is done under poor radio conditions to achieve good quality.
System
designs are based on trying to achieve either goal or a little of both
LTE ARCHITECTURE
Mobility
Management Entity (MME)
–MME is a controller
at each node on the LTE access network. At UE in idle state (idlemode), MME is responsible
for tracking and paging procedure which includes retransmission therein.
–MME is responsible
for selecting SGW (Serving SAE Gateway) which will be used during initial attach
EU and the EU time to do intra-LTE handover.
–Used for bearer control, a different viewR99/4 whichis
still controlled by the gateway
Serving
SAE Gateway (SGW)-Set
the path and forwards the data in the form of packets of each user-As an anchor
/ liaison between the UE and the eNBat the time of the inter handover-As a
liaison link between the 3GPP LTE technology with the technology
(in this case the 2G and 3G)
Gateway
Packet Data Network (PDN GW)
-Provides
for the UE 's relationship to the network packet-Provide a link relationship
between LTE technology with technology
non 3GPP (WiMAX) and 3GPP2 (CDMA 20001X and EVDO)
The MME Function
- NAS signalling;
- NAS signalling security;
- AS Security control;
- Inter CN node signalling for mobility between 3GPP access networks;
- Idle mode UE Reachability (including control and execution of paging retransmission);
- Tracking Area list management (for UE in idle and active mode);
- PDN GW and Serving GW selection;
- MME selection for handovers with MME change;
- SGSN selection for handovers to 2G or 3G 3GPP access networks;
- Roaming;
- Authentication;
- Bearer management functions including dedicated bearer establishment;
- Support for PWS (which includes ETWS and CMAS) message transmission.
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.
Subscribe to:
Posts (Atom)