WCDMA OVE RVIE W
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
WCDMA
O V E R V I EW
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
UMTS TERRESTRIAL RADIO ACCESS NETWORK (UTRAN) ARCHITECTURE
New Radio Access network needed mainly due to new radio access technology
Core Network (CN) is based on GSM/GPRS
Radio Network Controller (RNC) corresponds roughly to the Base Station Controller (BSC) in GSM
Node B corresponds roughly to the Base Station in GSM
Term “Node B” is a relic from the first 3GPP releases
RNC
NodeB
NodeB
NodeB
UE
CN
RNC
UE
Uu interface
Iub interface
Iur interface
UTRAN
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
UMTS TERRESTRIAL RADIO ACCESS NETWORK (UTRAN) ARCHITECTURERadio network controller (RNC) Owns and controls the radio resources in its domain Radio resource management (RRM) tasks include e.g. the following
Mapping of QoS Parameters into the air interface Air interface scheduling Handover control Outer loop power control Call Admission Control Setting of initial powers and SIR targets Radio resource reservation Code allocation Load Control
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
UMTS TERRESTRIAL RADIO ACCESS NETWORK (UTRAN) ARCHITECTURENode B Main function to convert the data flow between Uu and Iub interfaces Some RRM tasks:
Measurements Inner loop power control
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
RADIO PROPAGATION AND FADINGA transmitted radio signal
goes through several changes while traveling via air interface to the receiver
reflections, diffractions, phase shifts and attenuation
Due to length difference of the signal paths, multipath components of the signal arrive at different times to the receiver and can be combined either destructively or constructively
Depends on the phases of the multipath components
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
POWER CONTROL IN WCDMA1. Open loop power control
• Only for the initial power setting of the MS• Based on distance attenuation estimation from the downlink pilot signal
2. Inner loop transmitter power control (CL TPC) at a rate of 1500 Hz• Mitigates fading processes (fast and slow fading)• Tx power is adjusted up/down to reach SIR target• Both in UL and DL• Uses quality targets in MS / BS
3. Outer loop PC at the rate of 100 Hz• Sets the quality target used by the inner loop PC• Compensates the changes in the propagation conditions • Adjusts the quality target• Both in UL and DL
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
POWER CONTROL IN WCDMAInner loop power control in the uplink Outer loop PC (running in the radio network controller, RNC) defines
SIR target for the BS. If the measured SIR at BS is lower than the SIR-target, the MS is
commanded to increases its transmit power. Otherwise MS is commanded to decrease its power
Power control dynamics at the MS is 70 dB
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
POWER CONTROL IN WCDMAInner loop power control in downlink: Outer loop PC (running in the MS) defines SIR target for the MS If the measured SIR at the MS is lower than the SIR-target, the BS is
commanded to increases its transmit power for that MS. Otherwise, BS is commanded to decrease its power.
Power control rate 1500 Hz Power control dynamics is dependent on the service There’s no near-far problem in DL due to one-to-many scenario.
However, it is desirable to provide a marginal amount of additional power to mobile stations at the cell edge, as they suffer from increased other-cell interference.
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
DIVERSITY Time
Same information is transmitted in different times
Receive antenna Transmission is received with multiple antennas Power gain and diversity gain
Transmit antenna Transmission is sent with multiple antennas
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
WCDMA HANDOVERSWCDMA handovers can be categorized into three different types Intra-frequency handover WCDMA handover within the same frequency and system. Soft, softer and
hard handover supportedInter-frequency handover Handover between different frequencies (carriers) but within the same
system E.g. from one WCDMA operator to another Only hard handover supportedInter-system handover Handover between WCDMA and another system, e.g. from WCDMA to GSM Only hard handover supported
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
WCDMA HANDOVERSSoft handover Handover between different Node
Bs Several Node Bs transmit the
same signal to the UE which combines the transmissions Advantages: lower Tx power
needed for each Node B and UE lower interference, battery
saving for UE Disadvantage: resources (code,
power) need to be reserved for the UE in each Node B Excess soft handovers limit
the capacity No interruption in data
transmission Needs RNC duplicating frame
transmissions to two Node Bs
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
WCDMA HANDOVERSSofter handover Handover between two sectors of the
same Node B Special case of a soft handover No need for duplicate frames
Hard handover The source is released first and then
new one is added Short interruption in data flow
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
WCDMA HANDOVERSSome terminology Active set (AS), represents the Node Bs to which the UE is in soft
handover Neighbor set (NS), represents the links that UE monitors but which
are not already in active set
Received signal strength
BS1
BS2
Threshold_1
Triggering time_1
Threshold_2
Triggering time_2
BS2 from the NS reaches the threshold to be added to the AS BS2 is still after the
triggering time above threshold and thus
added to the AS
BS1 from the AS reaches the threshold to be dropped from
the AS
BS1 dropped from the AS
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
CAPACITY AND COVERAGEIn WCDMA coverage and capacity are tight together: When the load increases, the interference levels increases, too, and
therefore also increased transmit powers are needed in order to keep constant quality.
Due to finite power resources, the more users Node B serves the less power it has for each UE coverage will decrease
This leads to cell breathing: the coverage area changes as the load of the cell changes.
• Therefore, the coverage and the capacity have to be planned simultaneously
• Radio resource management (RRM) is needed in WCDMA to effectively control cell breathing.
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
CAPACITY AND COVERAGEReceived power of one user as
a function of users per cell
Due to finite maximum Tx power of the UE coverage is usually limited by the uplink
Node B does not have this problem
There is enough Tx power to transmit very far to a single user if necessary
However, downlink Tx power is divided between all users and thus capacity is limited by the downlink
05/02/2023
M D . J OY N A L A B A D E N ( J OY N A L A B A D E N @ G M A I L . C O M )
ADVANCED RECEIVERS WITH HSDPAUE receiver experiences significant interference from different
sources In a reflective environment the signal interferes itself Neigboring base station signals interfere each other One solution to decrease mainly own base station signal interference
is to use an equalizer before despreading
Own cell interference
Other cell interference
Own signal
Related Documents
