EPL 657 Topic 7: WCDMA- Radio Resource Management · PDF fileTopic 7: WCDMA- Radio Resource...
Transcript of EPL 657 Topic 7: WCDMA- Radio Resource Management · PDF fileTopic 7: WCDMA- Radio Resource...
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EPL 657
Topic 7: WCDMA- Radio
Resource Management
ΕΠΛ657
Τμήμα Πληροφορικής
Πανεπιστήμιο Κύπρου
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Lecture Overview
Capacity, coverage, and QoS tradeoffs.
RRM aims and functionality
Preliminaries
Handover control.
Power control.
Admission control.
Packet scheduling.
Load Control.
Interworking and dependencies
Heterogeneous networks and handovers
CDMA codes
WCDMA
RRM aims and functionality
basics
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Capacity, coverage and Qos tradeoffs Resource Management purpose.
Ensure planned coverage for each service, plus maximise capacity.
Ensure required connection quality.
Ensure planned (low) blocking.
Optimize the system usage in run time.
Real time Resource Management and Optimization functions. Interference measurements.
Soft capacity utilization.
Scheduling in radio interface.
Actions to load change.
Real time interference minimization strategies: Handover control.
Service prioritization.
Connection parameter settings.
Admission control.
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RRM aims and functionality Aim
optimization of the radio interface utilization (maximise capacity and coverage), considering the differences among the different services, not only in terms of QoS requirements but also in terms of the nature of the offered traffic, bit rates, etc.
The RRM functions include: 1. Admission control:
it controls requests for setup and reconfiguration of radio bearers.
2. Congestion control: it faces situations in which the system has reached a congestion status
and therefore the QoS guarantees are at risk due to the evolution of system dynamics (mobility aspects, increase in interference, etc.).
3. Mechanisms for the management of transmission parameters: are devoted to decide the suitable radio transmission parameters for
each connection (i.e. TF, target quality, power, etc.).
4. Code management: for the downlink it is devoted to manage the OVSF code tree used to
allocate physical channel orthogonality among different users.
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Radio Resource Management (RRM)
RRM contains various algorithms, which aim to stabilize the radio path enabling it to fulfill the QoS criteria set by the service (e.g. Conversational, Streaming, Interactive, Background) using the radio path.
The RRM algorithms must deliver information over the radio path, which is named UTRA Service.
The RRM algorithms are:
Handover Control
Power Control
Admission Control (AC), Packet Scheduling and Code Management
The control protocol used for this purpose is the Radio Resource Control (RRC) protocol.
Radio Resource Management (RRM)
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RRM responsibility is taken care of by UTRAN. RRM is located in both UE and RNC inside UTRAN.
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RRM methods
Connection based functions: Power Control (PC).
Needed to keep the interference levels at minimum in the air interface and to provide the required quality of service.
Handover Control (HC). Provide continuity of mobile services to a user traveling over cell boundaries in a cellular
infrastructure.
Network based functions: Admission control (AC).
Handles all new incoming traffic. Check whether new connection can be admitted to the system.
Occurs when new connection is set up as well during handovers and bearer modification.
Load control (LC). Manages situation when system load exceeds the threshold and some counter measures
have to be taken to get system back to a feasible load.
Packet scheduling (PS). Handles all Real and Non Real time traffic, (packet data users). It decides when a packet
transmission is initiated and the bit rate to be used.
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WCDMA radio network control
In WCDMA QoS will be controlled by:
Radio Network Planning. (Network Parameters.)
Real time RRM (Radio Resource Management) operations in RNC BS.
Real time power control.
Drift RNC
Handover
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Handover
basic concept when subscriber moves from coverage area of one cell to another, a
new connection with new target cell has to be set-up and the connection with the old cell may be released.
many reasons why handover needs to be activated. basic reason is air interface connection between the UE and UTRAN
does not fulfil the QoS criteria set for that connection (RAB) and thus the UE or the UTRAN initiates actions in order to improve the connection.
number of handovers depends on UE mobility. the faster the UE is moving, the more handovers it causes to UTRAN.
to avoid undesirable handovers, UE with high motion may be handed over from micro cells to macro cells. In case UE is not moving or moving slowly, it can be handed over from macro cells to micro cells.
decision to perform a handover always made by RNC that is currently serving subscriber,
except for the handover of traffic reasons which in that case the Mobile Switching Centre (MSC) will make the decision.
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Handover
Depending on diversity used in association with handover mechanisms, can be categorized as: Hard handover
means that all old radio links in the UE are removed before new radio links are established. Therefore there are not only lack of simultaneous signals but also there is a very short cut in the connection
Soft handover performed between two cells belonging to different BSs, but not necessarily to the same
RNC.
RNC involved in soft handover must co-ordinate the execution to the soft handover over the Iur Interface.
Soft handover means that the radio links are added and removed in a way that the UE always keeps at least one radio link to the UTRAN.
Soft handover is performed by means of macro diversity, which refers to the condition that several radio links are active at the same time. In a soft handover event, the source and the target cells have the same frequency
Softer handover special case of soft handover where radio links that are added and removed from the
Active Set belong to the same Node B. The BS transmits through one sector but receives more than one sector. In this case the UE has active uplink radio connections with the network through more than one sector populating the same BS.
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Handover (HO)
The Handover process is one of the essential means that guarantees user mobility in a mobile communication network, by supporting continuity of service. intra-system handovers
intra-frequency
inter-frequency
inter-system handovers.
When a handover occurs, many RRM mechanisms are triggered other than the actual Handover mechanism. AC handles the downlink admission decision (acceptance and queuing)
LC updates downlink load information when a new HO link is admitted
PS releases codes for HO branches of NRT and schedules HO addition requests for NRT
RM: Activates/deactivates HO brances. Allocates/releases DL spreading codes.
The HO mechanism processes the measurements made by a terminal and makes decisions. It also updates reference transmission powers.
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Handover Reasons The basic reason behind a HO is that the air interface does not fulfil the
desired criteria set for it anymore and thus either the UE or the UTRAN initiates actions in order to improve the connection.
The HO execution criteria depend mainly upon the HO strategy implemented in the system. Signal Quality
Constant signal measurements carried out by both the UE and the Node B aim to detect any signal deterioration.
When the quality or the strength of the radio signal falls below certain parameters set by the RNC, a HO is initiated. This holds for both the UL and the DL radio links.
Traffic level HO is also initiated when the intra-cell traffic is approaching the maximum cell
capacity or a maximum threshold.
The HO usually occurs when the UE approaches the edges of the cell with high load.
This sort of HO helps to distribute the system load more uniformly and to adapt the needed coverage and capacity efficiently meeting the traffic demand within the network.
User mobility The number of HOs is proportional to the degree of UE mobility.
To avoid undesirable HOs, UE’s with high motion speed may be handed over from micro cells to macro cells. In the same way, UE’s moving slowly or not at all, can be handed over from macro cells to micro cells.
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Handover Process
A basic HO process consists of three main phases measurement phase
Intra-frequency
Inter-frequency
Traffic volume
Quality
Internal
decision phase Change of best cell.
Changes in the SIR level.
Changes in the ISCP level.
Periodical reporting.
Time-to-trigger.
execution phase. Network Evaluated Handover (NEHO)
Mobile Evaluated Handover (MEHO)
MEASUREMENT
DECISION
EXECUTION
Measuremetnt criteria
Measurement reports
Algorith parameters
Handover criteria
Handover signalling
Radio Resource Allocation
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Handover in UMTS
(1) (2) (3) time
Sig
nal S
trength
Upper threshold
Lower threshold
Handover Margin
Signal BSignal A
Summed Signal
Cell A Cell B
Signal A equals lower threshold. Based on UE measurements, RNC
recognises an available neighbouring signal (signal B), with adequate strength to improve quality of connection. RNC adds signal B to Active Set.
UE has two simultaneous connections to UTRAN and benefits from summed signal (signal A + B)
When quality of signal B becomes better than signal A RNC keeps this as starting point for
HO margin calculation.
Signal B greater than defined lower threshold. strength adequate to satisfy
required QoS.
strength of summed signal exceeds defined upper threshold, causing additional interference. RNC deletes signal A from Active Set.
Handover Algorithm
Assumption: a UE, currently connected to
signal A, is located in cell A and moving
towards cell B.
Pilot signal A, deteriorates, approaching
lower threshold Handover Triggering
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Mobility and Handover Issues – Support of
mobility in UTRAN: Macrodiversity
Multicasting of data via several
physical channels
Enables soft handover
FDD mode only
Uplink
Simultaneous reception of UE data
at several Node Bs
Reconstruction of data at Node B,
SRNC or DRNC
Downlink
Simultaneous transmission of data
via different cells
Different spreading codes in different
cells
CN Node B RNC
Node B UE
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Mobility and Handover Issues – Soft Handover Algorithm (Macrodiversity)
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Mobility and Handover Issues – Soft Handover Algorithm example
By the term Soft Handover we mean that the mobile
node is maintaining connections with more than one
base stations.
The Active Set includes the cells that form a soft
handover connection to the mobile station.
The Neighbor/Monitored Set is the list of cells that the
mobile station continuously measures, but their signal
strength is not powerful enough to be added to the
Active Set.
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SHO Algorithm
The algorithm samples the
signal strength of the
surrounding base stations
every 1 sec
Uses 3dB as the threshold
for soft handover and
Uses 6dB as the threshold
for hard handover.
The size of the Active Set is
3 signals.
1. Each UE is connected to its Primary_BS, and
keeps an Active_ Set (2 “closest” cells)
2. Each UE measures the SIR received from
the surrounding cells.
3. If (AS1_SIR – Pr_BS_SIR) >3dB OR
(AS2_SIR – Pr_BS_SIR) > 3dB
i. UE enters Soft Handover
ii. UE keeps a simultaneous connection to the
Primary_BS and one or both of the Active_Set
cells
4.
i. If (AS1_SIR – Pr_BS_SIR) > 6dB for three measurements in a row: AS1 becomes the Primary_BS
ii. If (AS2_SIR – Pr_BS_SIR) > 6dB for three
measurements in a row: AS2 becomes the
Primary_BS
5. Neighboring cells replace the cells in the
Active_Set if their SIR exceeds the
Active_Set cells’ SIR by 6dB.
Relationship of RSSI, operating point,
sensitivity, SNR
21 http://ieee802.org/16/tutorial/T80216-02_04.zip
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Simulation example using OPNET
Handover Scenarios (1/2)
UE moving between two Node B’s
Objective: Conduct a performance comparison between soft and hard handover.
Soft vs. Hard Handover Scenario
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Simulation example using OPNET
Handover Scenarios (2/2) Results:
Application response time: No significant difference between soft and hard. Uplink Transmission Power of the Physical Channels: soft handover produces better results.
Simulation DEMO
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Handover Types (1/2) Soft Handover (a)
Takes place when a new connection is established before the old connection is released.
In Soft HO the neighbouring Node B involved in the HO transmits on the same frequency.
Soft HO is performed between two cells belonging to different Node B’s but not necessarily on the same RNC. The RNC involved in the Soft HO must co-ordinate the execution of the Soft HO over the Iur interface.
Softer Handover (b) When a new signal is either added to or deleted from the Active Set, or replaced by a stronger signal
within the different sectors under the same Node B
The Node B transmits through one sector but receives from more than one sector.
Soft-Softer Handover When soft and softer HOs occur simultaneously.
A soft-softer HO may occur for instance, in association with inter-RNC HO, while an inter-sector signal is added to the UE’s Active Set along with adding a new signal via another cell controller by another RNC.
Sector 1
f1
Sector 2
f1
B
SUE
Sector 3
f1
Multipath signal
through Sector 1 Multipath signal
through Sector 3
Frequency
f1
Frequency
f1
BS BS
UE
(a) (b)
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Handover Types (2/2) Hard Handover
During the HO process, the old connection is released before making a new connection.
Lack of simultaneous signals
Very short cut in the connection, which is not distinguishable for the mobile user.
Intra-frequency hard handover (a) the new carrier, to which the UE is accessed after the HO procedure is the same as the original
carrier
Inter-frequency hard handover (b) the carrier frequency of the new radio access is different from the old carrier frequency to which
the UE is connected.
Frequency
f1
Frequency
f1
BS BS
UE
(a) (b)
RNCRNC
Iur
Frequency
f1
Frequency
f2
BS BS
UE
Power control
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Power control (PC)
In mobile communication systems such as 3G systems, which are based on the WCDMA technique where all users can share a common frequency, interference control is a crucial issue.
especially important for UL direction, since one UE located close to the Node B and transmitting with excessive power, can easily overshoot mobiles that are at the cell edge (the near-far effect), block the whole cell, or even cause interference to UEs in neighbouring cells (inter-cell interference). main target is to mitigate near-far problem by making the transmission power
level received from all terminals as equal as possible at the home cell.
Due to its critical nature in WCDMA (WCDMA is interference-limited), the power control for the connection is applied 1500 times per second.
in DL direction system capacity is directly determined by required code power for each connection. Therefore, essential to keep transmission powers at a minimum level while ensuring adequate signal quality and level at the receiving end.
Power control (PC)
In W-CDMA a group of functions is introduced for this purpose. They are summarised as PC. PC consists of:
open-loop PC, responsible for setting the initial UL and DL transmission powers when a UE is accessing the network
inner-loop PC (also called fast closed-loop PC), adjusts the transmission powers dynamically on a 1500 Hz basis, using a target SIR
outer-loop PC in both the Uplink (UL) and the Downlink (DL) directions, estimates the received quality and adjusts the target SIR (Signal to Interference Ratio) for the fast closed-loop PC so that the required quality is provided.
slow PC applied to the DL common channels.
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Power Control (PC)
To manage the power control properly in WCDMA, the system uses two different defined Power Control mechanisms: Open Loop Power Control (OLCP)
This kind of Power Control is useful for determining the initial value of transmitted power both Uplink and Downlink when a UE is accessing the Network.
Closed Loop Power Control (CLPC) Inner Loop Power Control (Also called as Fast Power Control)
Adjusts the transmission powers dynamically on a 1500 Hz basis based on the Target SIR (Set by the Outer Loop Power Control).
Compensate also for fast fading
Outer Loop Power Control
Estimates the received quality and adjusts the Target SIR for the fast closed-loop PC so that the required quality is provided.
These Power Control Mechanisms work together, in order to: Keep the Target SIR in acceptable level
Increase the terminal’s (UE) battery-life
Increase the overall system capacity (minimize interference)
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Interaction between PC algorithms
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Handover and Power Control Results
Cell 6
Cell 7
Cell 11
Cell 10
Admission control
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Admission Control (AC)
Decides whether new Radio Access Bearer (RAB) is admitted or not. Real-Time traffic admission to the network is decided.
Non-Real-Time traffic after RAB has been admitted the optimum scheduling is determined.
Used when the bearer is Set up.
Modified
During the handover.
Estimates the load and fills the system up to the limit.
Used to guarantee the stability of the network and to achieve high network capacity.
Separates admission for UL and DL. Load change estimation is done in the own and neighbouring cells.
RAB admitted if the resources in both links can be guaranteed.
In decision procedure AC will use thresholds set during radio network planning.
The functionality located in the RRM of the RNC.
Representative proposed CAC types
Throughput based AC
Wideband Power based AC
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Logical Dependencies of AC AC has some logical dependencies due to its interworking with the rest of the
RRM mechanisms. receives load information from PS and LC.
receives information about the UE active set from the HC
sends PS information about the radio bearers.
sends load changes informations to LC.
sends the target values for BER, BLER and SIR to PC
Load Control
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Load Control
Under normal circumstances the LC ensures system stability and that the network does not enter an overload state. In order to achieve stability the LC works with the CAC and with the Packet Scheduler (PS). This task is called preventive LC.
Only in special circumstances can the system be found in a situation of overload. When this happens the LC is responsible for reducing the load in a relatively fast way, bringing the system back to the desired state of operation. This state of operation is defined during the RNP process.
The LC process is distributed between two types of network elements, the Node B and the RNC.
The actions that can be taken with the objective of reducing the load are:
Actions for fast LC located in the Node B: Denying the DL or overriding the UL Transmit Power “up” commands.
Lowering the reference SIR for the inner-loop PC in the UL.
Actions for LC located in the RNC: Interacting with the Packet Scheduler and reducing the packet data traffic.
Reducing the bit rates of RT users, e.g., voice services.
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Load Control (LC) The purpose of the LC mechanism is to increase the capacity of a cell and
prevent overload continuously measures uplink and downlink interference
In an overload condition, reduces the load and brings the network back into operating state
normal state the power received in the uplink and the transmitted power in the downlink are a target
value which is the optimal average of the PrxTotal and PtxTotal for the uplink and downlink.
preventive state the PrxTotal in the uplink and PtxTotal in the downlink are below PrxTarget and
PtxTarget respectively, plus an Offset value which equals the maximum margin by which the target value can be exceeded.
LC ensures that the network is not overloaded and remains stable
overload state Anything above the preventive state
LC is responsible for reducing the load and bringing the network back into operating state. The actions that can be taken with the objective of reducing the load are: Actions for fast LC located in the Node B:
Denying the DL or overriding the UL Transmit Power “up” commands.
Lowering the reference SIR for the inner-loop PC in the UL.
Actions for LC located in the RNC: Interacting with the Packet Scheduler and reducing the packet data traffic.
Reducing the bit rates of RT users, e.g., voice services.
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Power Based LC algorithm
BS Reports
PrxTotal
RNC Updates
Cell Load
Exceeds
Pr/tx target
Load Control Checks
Cell Load
No Actions
No
Exceeds Pr/tx target
+ Pr/tx Offset
Preventive Actions
PS and ACFast LC actions in BTS:
- Deny (DL) or overwrite (UL) Tx Power
Control 'up' commands.
- Lower SIR target for UL inner loop PC.
LC actions located in the RNC:
- Interact with PS and throttle back packet
data traffic.
- Lower bit rates of RT users.
- Drop single calls in a controlled manner.
No
Yes
Yes
Packet scheduling
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Packet Scheduling
The Packet Scheduling controls the UMTS packet access and is located in the RNC. The functions of the PS are: To determine the available radio interface resources for Non Real
Time radio bearers.
To share the available radio interface resources between Non Real Time radio bearers.
To monitor the allocation for Non Real Time.
To initiate transport channel type switching between common and dedicated channels when necessary.
To monitor the system loading.
To perform LC actions for Non Real Time radio bearers when necessary.
Packet Scheduling
AC and PS both participate in the handling of Non Real Time radio bearers. AC takes care of admission and release of radio access bearers (RABs).
Radio resources are not reserved for the whole duration of the connection but only when there is actual data to transmit.
PS allocates appropriate radio resources for the duration of a packet call, i.e., active data transmission.
PS is done on a cell basis. Since asymmetric traffic is supported and the load may vary a lot
between UL and DL, capacity is allocated separately for both directions.
PS can decide the allocated bit rates and the length of the allocation. In W-CDMA this can be done in different ways, like code division, time division or power based
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Packet Scheduling
The cell’s radio resources are shared between RT and NRT radio bearers. The proportion of RT and NRT traffic fluctuates rapidly.
A characteristic of the load caused by RT traffic is that it cannot be efficiently controlled. The load caused by RT traffic, interference from other cell users and noise, is called Non-
controllable load.
The remaining free capacity from the Planned Target Load can be used for NRT radio bearers on a best effort basis. The load caused by best effort NRT traffic is called the Controllable load.
Load
time
Free capacity, which can be
allowed for controllable load
on best effort basis
Non controllable load
Planned Target Load
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PS - Time Division Scheduling
Time Division Scheduling The available capacity is allocated to one or very few radio bearers at a time.
The allocated bit rate can be very high and the time needed to transfer the data in the buffer is short.
The allocation time can be limited by setting the maximum allocation time, which prevents one high bit rate user from blocking others.
Scheduling delay depends on load, so that the waiting time before a user can transmit data is longer when the number of users is higher.
Time division scheduling is typically used for DSCH where the scheduling of PDSCH can happen on a resolution of one 10ms radio frame, but it can also utilised for DCH scheduling.
Us
er
1
Us
er
2
Us
er
3
Us
er
4
Us
er
1
Us
er
3
Us
er
2
Us
er
4
bit rate
time
Us
er
1
Us
er
2
Us
er
3
Us
er
4
Us
er
1
Us
er
3
Us
er
2
Us
er
4
bit rate
time
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PS - Code Division Scheduling
The available capacity is shared between large numbers of radio bearers, allocating low bit rate simultaneously for each user.
In code-division scheduling all users are allocated a channel when they need it. Allocated bit rates depend on load, so that the bit rates are lower when the number of users is higher.
Establishment and release delays cause smaller losses in capacity due to the lower bit rates and long time transmissions.
Due to the lower bit rate, allocation of resources takes longer in code division scheduling than in time division scheduling. air interface interferences levels are more predictable and can be seen as an
advantage for code division scheduling.
bit rate
User 1
User 2
User 3
User 4
time
bit rate
User 1
User 2
User 3
User 4
time
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PS - Transmission Power based Scheduling
The allocated packet data rate could be based on the required transmission power of the connection Higher bit rates for a users requiring less transmission power per
transmitted bit. Minimization of the average required transmission power per bit,
the transmitted interference generated in the network,
increase of the average cell throughput compared to equal bit rate scheduling.
Transmission power based scheduling gives more gain in the average throughput in DL than in UL compared to equal bit rate scheduling. In the UL, typically at least 50% of the interference originates from the
users within the same cell, and that interference does not depend on the transmission power but only on the received powers.
In the DL the transmission power based scheduling can clearly increase the average DL throughput.
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PS - Packet Scheduling with QoS Differentiation
and Round Robin
Packet Scheduling with QoS Differentiation
This algorithm is based on the differentiation of users in terms of QoS the network operators will be able to offer different services to the users.
The knowledge of the Carrier over Interference (C/I) can increase the CDMA capacity by transmitting mostly when channel conditions are favourable By giving certain users and services high priority, the capacity of the system is increased
at the expense of degraded QoS for the rest of the users.
Round Robin Users get an equal share of the radio resources and the QoS will be fairer distributed
among them.
In order to get the QoS 100% fairly distributed among users, the users in degraded conditions should get a larger share of the resources than users in good conditions.
This is the inverse C/I scheduling. By taking the radio conditions into account one can modify the PS, so that it goes from being C/I based to inverse C/I based.
Interworking between
different functionalities and
dependancies
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Interworking actions of AC, PS, and LC
In uplink. PrxTarget, the optimal average PrxTotal
PrxOffset, the maximum margin by which PrxTarget can be exceeded.
In downlink. PtxTarget , the optimal average for PtxTotal.
PtxOffset , the maximum margin by which PtxTarget can be exceeded.
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Summary: Resource Management (RM)
Purpose: to allocate physical radio resources when requested by the RRC layer.
Knows radio network configuration and state data.
Sees only logical radio resources. Allocation is a reservation of proportion of the available radio
resources according to the channel request from RRC layer for each radio connection.
Input comes from AC/PS.
RM informs PS about network conditions.
Allocates scrambling codes in UL.
Allocates the spreading codes in downlink direction. Able to switch codes and code types
During soft handover.
Defragmentation of code tree.
Codes in UMTS/CDMA
Overview
Access Schemes
CDMA Coding/Spreading
CDMA Codes
Code Trees
Summary of Code Characteristics
Recall: Access Schemes In radio systems there are two kinds of resources:
Frequency
Time
Access per frequency Division by frequency results in Frequency Division Multiple Access (FDMA)
In FDMA each pair of communicators is allocated part of the spectrum for all of the time
Access per time Division by time results in Time Division Multiple Access (TDMA)
In TDMA each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time
In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections.
UMTS Access done using CDMA
CDMA Coding/Spreading CDMA uses unique spreading codes to spread the baseband
data before transmission
Assume that user data is a bit sequence of rate R
CDMA spreading is a process of multiplying each user data bit with a sequence of n (e.g. 8) code bits, called chips
The resulting spread data is at a rate of n x R, which is transmitted across the wireless channel
The increase of signaling rate by a factor of n corresponds to a widening of the occupied spectrum of the spread user signal
De-spreading restores a bandwidth proportional to R for the signal
The rate of a spreading code is referred to as chip rate rather than bit rate.
Channelization Code Scrambling Code
Bit Rate Chip Rate Chip Rate
DATA
CDMA Codes
Transmission from a single source are separated by
channelization codes (based on spreading)
The channelization codes are based on the Orthogonal
Variable Spreading Factor (OVSF) technique
The codes are picked from a code tree
Different terminals and different base stations may operate
their code trees independently from each other
The downlink orthogonal codes within each base
station are managed by the Radio Network
Controller (RNC)
CDMA Codes
Orthogonal variable spreading factor (OVSF) is an implementation
of Code division multiple access (CDMA) where before each signal is
transmitted, the spectrum is spread through the use of a user's code.
User's codes are carefully chosen to be mutually orthogonal to
each other.
These codes are derived from an OVSF code tree, and each user is
given a different, unique code. An OVSF code tree is a complete
binary tree (a tree data structure in which each node has at most two
children) that reflects the construction of Hadamard matrices
(a Hadamard matrix is a square matrix whose entries are either +1 or −1 and
whose rows are mutually orthogonal.).
Code Trees
Length of the OVSF Channelization codes may vary between 4 and 512 chips
The closer we get to the root, the higher the bitrates assigned
Once a code is assigned, the options found in the sub-tree that has the code as a root are no longer available
Summary of Code Characteristics
OVSF Channelization Codes
Usage Uplink: Separation of physical data and
control channels from same terminal
Downlink: Separation of downlink connections
to different users within one cell
Length UL: 4-256 chips
DL: 4-512 chips
Number of Codes Number of codes equals the spreading factor
(under one scrambling code)
Code Family Orthogonal Variable Spreading Factor
Spreading Exists and increases the transmission
bandwidth
Heterogeneous networks and
handover (Media
Independent Handover)
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The Use Case
My Desk Undocked & walking
around
Headed out of the
building
802.3 802.11 802.16
Internet
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Need for Handovers :Types of Handovers
Homogeneous (Horizontal) Handovers Within Single Network (Localized Mobility)
802.11r, 802.16e, 3GPP, 3GPP2
Limited opportunities
Heterogeneous (Vertical) Handovers Across Different Networks (Global Mobility)
More Opportunistic
IEEE 802.21 is primarily for Vertical Handovers
….can also be used for Homogeneous Handovers
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Need for Handovers : Genesis for 802.21
Handover
Initiation
Handover
Preparation
Handover
Execution
Search New
Link
Network Discovery
Network Selection
Handover Negotiation
Setup New
Link
Layer 2 Connectivity
IP Connectivity
Transfer
Connection
Handover Signaling
Context Transfer
Packet Reception
IEEE 802.21 helps with Handover Initiation,
Network Selection and Interface Activation
Scope of 802.21
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Need for Handovers: Handover Standards
IEEE
802.11r
802.16e
3GPP/2
VCC I-WLAN
SAE-LTE
Horizontal
Handovers
IP Mobility & Handover
Signaling
Inter-working &
Handover Signaling
IEEE
802.21
Provides 802 component to other Handover Standards
IETF
MIP
FMIP SIP
HIP NETLMM
DNA MIPSHOP
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IEEE 802.21 Standard
Media Independent Handover Services
Optimize Layer 3 and above Handovers – Across 802 Networks and extend to Cellular Networks
– (802.3 <> 802.11 <> 802.16 <> Cellular)
Key Benefits – Optimum Network Selection
– Seamless Roaming to Maintain Connections
– Lower Power operation for Multi-Radio devices
For More Information: www.ieee802.org/21
65
802.21
Information
Server
Media Independent Information Service
WMAN
WLAN
WWAN
Network
Type
SSID/ Cell
ID
BSSID Operator Security NW Channel QoS Physical
Layer
Data Rate
GSM 13989 N/A AT&T NA NA 1900 N/A N/A 9.6 kbps
Network
Type
SSID/
Cell ID
BSSID Operator Security NW Channel QoS Physical
Layer
Data Rate
GSM 13989 N/A AT&T NA NA 1900 N/A N/A 9.6 kbps
802.11b Intel 00:00:… Intel .11i EAP-PEAP 6 .11e OFDM 11 Mbps
Network
Type
SSID/
Cell ID
BSSID Operator Security EAP Type Channel QoS Physical
Layer
Data Rate
GSM 13989 N/A Oper-1 NA NA 1900 N/A N/A 9.6 Kbps
802.11n Enterprise 00:00:… Oper-2 .11i EAP-PEAP 6 .11e OFDM 100 Mbps
802.16e NA NA Oper-3 PKM EAP-PEAP 11 Yes OFDM 40 Mbps
Global Network Map
•List of Available Networks - 802.11/16/22, GSM, UMTS
•Link Layer Information
- Neighbor Maps
•Higher Layer Services
- ISP, MMS, ….
Some preliminaries
66
67
Radio Resource Control Procedures
Within the UMTS architecture, RRM algorithms will be carried out in the Radio Network Controller (RNC).
Decisions taken by RRM algorithms are executed through Radio Bearer Control Procedures (a subset of Radio Resource Control Procedures):
1. Radio Bearer Set-up.
2. Physical Channel Reconfiguration.
3. Transport Channel Reconfiguration.
Radio bearer and channels
Radio Bearer:
Whenever a certain service should be provided under certain guarantees QoS a
bearer service with clearly defined characteristics and functionality must be set up
from the source to the destination of the service, maybe including not only the
UMTS network but also external networks
Physical layer Interfaces medium access control (MAC) sub layer of layer 2 and the radio
resource control (RRC) layer of layer 3. The physical layer offers different transport channels to MAC. A transport channel is characterized by how the information is transferred over the radio interface.
Transport channels are channel coded and then mapped to the physical channels specified in the
physical layer. MAC offers different logical channels to the radio link control (RLC) sub layer of layer 2.
A logical channel is characterized by the type of information transferred. Layer 2 is split into
following sub layers: MAC, RLC, packet data convergence protocol (PDCP) and broadcast/multicast control (BMC). Layer 3 and RLC are divided into control and user planes. PDCP and BMC exist in the user plane only.
68
Bearer services
69
70
Power Control (PC)
The Near-Far Problem:
MS1 and MS2 operate within the same frequency, separable at the base station only by their respective spreading codes.
MS1 at the cell edge suffers a path loss, say 70 dB above that of MS2 which is near the base station BS.
If there were no mechanism for MS1 and MS2 to be Power Controlled to the same level at the Base Station, MS2 could easily over shout MS1 and thus block a large part of the cell The optimum strategy in the sense of maximizing capacity is to equalize the received power per bit of all
mobile stations at all times (Target SIR).
71
Open Loop Power Control
The UL and DL frequencies of W-CDMA are within the same
frequency band
a significant correlation exists between the average path-loss of the two
links.
This makes it possible for each UE prior to accessing the network,
and for each Node B when the radio link is set up, to estimate initial
transmit powers needed in UL (from UE to Node B) and DL based
(from Node B to UE) on path-loss calculations in the DL direction.
UE adjusts the power based on an estimate of the received signal level for the BS
CPICH (Common Pilot Channel) when the UE is in idle mode and prior to
Physical Random Access Channel (PRACH) transmission.
In addition to that, the UE receives information about the allowed power
parameters from the cell’s Broadcast Common Channel (BCCH) when in idle
mode.
UE evaluates the path loss occurring and based on this difference together with
figures received from the BCCH and the UE it is able to estimate what might be
an appropriate power level to initialize the connection.
72
Uplink Open Loop Power Control The UL open-loop PC function is located both in the UE and in the UTRAN.
Based on the calculation of the open-loop PC, the terminal sets the initial power for the first Physical Random Access Channel (PRACH) preamble and for the UL Dedicated Physical Control Channel (DPCCH) before starting the inner-loop PC.
Preamble_Initial_Power = CPICH_Tx_power - CPICH_RSCP + UL_interference + UL_required_CI
RSCP: Received Signal Code Power
CPICH: Common Pilot Channel
The same procedure is followed by the UE when setting the power level of the first Physical Common Packet Channel (PCPCH) access preamble.
When establishing the first DPCCH, the UE starts the UL inner-loop PC at a power level according to
DPCCH_Initial_Power = DPCCH_Power_offset - CPICH_RSCP
CPICH_RSCP is measured by the terminal.
DPCCH_Power_offset is calculated by AC in the RNC and provided to MS during a radio bearer or physical channel reconfiguration.
DPCCH_Power_offset = CPICH_Tx_power + UL_interference + SIRDPCCH -10log (SFDPDCH)
SIRDPCCH is the initial target SIR produced by the AC for that particular connection
SFDPDCH is the spreading factor of the corresponding Dedicated Physical Data Channel (DPDCH).
73
Downlink Open Loop Power Control
This function is located in both the UTRAN and the UE
In the Downlink, the open-loop PC is used to set the initial power of the downlink channels based on the DL measurement reports from the UE.
A possible algorithm for calculating the initial power value of the DPDCH when the first hearer service is set up is
R is the user bit rate
(Eb/No)DL is the DL planned Eb/No value set during the RNP W is the chip rate
(Ec/No)CPICH is reported by the UE
α is the DL orthogonality factor
Ptx_Total is the carrier power measured at the Node B and
reported to the RNC.
Ec/No: Ratio of desired receive power per chip to receive power density in the band
)_)/(
__(
)/(TotalPtx
NoEc
powerTxCPICH
W
NoEbRP
CPICH
DLInitial
Tx
74
Power Control on Downlink Common Channels
Determined by the network.
The ratio of the transmit powers between different
downlink common channels is not specified in the
recommendations.
DL common channel Typical power level Note
P-CPICH
P-SCH and S-SCH
P-CCPCH
PICH
AICH
S-CCPCH
30-33 dBm
-3 dB
-5 dB
-8 dB
-8 dB
-5 dB
5-10% of maximum cell Tx power (20 W)
relative to P-CPICH power
relative to P-CPICH power
relative to P-CPICH power and Np = 72
power of one Acquisition Indicator (AI)
compared to P-CPICH power
relative to P-CPICH and SF = 256 (15 kbps)
CPICH: Common Pilot Channel
75
Closed Loop Control
In contrast with Open Loop Power Control, Closed
Loop Power Control is utilized for adjusting the
power when the radio connection has already been
established.
Its main target its to compensate the effect of
rapid changes in the radio signal strength (due
to the radio path environment, mobility etc.) and
hence it should be fast enough to respond to these
changes.
Closed Loop Power Control, includes inner and
outer Loop Power Control.
76
Inner Loop Power Control In the case of uplink CLPC mechanism, the BS commands the
UE to either increase or decrease its transmission power with a cycle of 1.5 KHz (1500 times per second) with a fixed step size.
This decision whether to increase or decrease the power, is based on the received SIR estimated by the BS.
When the BS receives the UE signal it compares the signal strength with the pre-defined threshold value at the BS.
If the UE transmission power exceeds the threshold value, the BS sends a Transmission Power Command (TPC) to the UE to decrease its signal power.
If the UE transmission power is lower than the threshold target, the BS sends a TPC to the UE to increase its signal power.
77
Inner Loop Power Control
3. BS sends Transmission Power
Command (TPC). If X > Maximum
Threshold value then TCP (decrease) or
if X < Minimum Threshold vaIu Side
TCP (increase)
2. BE receives the Signal
transmitted from the UE
and estimates its Signal
Power. BS compares this
Power Signal X with the
pre-defined threshold
values in the BS.
1. UE transmits a signal with a Signal
Power level = X
4. UE adjust its
transmitting Power level
signal according to the
received TPC command
3. BS sends Transmission Power
Command (TPC). If X > Maximum
Threshold value then TCP (decrease) or
if X < Minimum Threshold vaIu Side
TCP (increase)
2. BE receives the Signal
transmitted from the UE
and estimates its Signal
Power. BS compares this
Power Signal X with the
pre-defined threshold
values in the BS.
1. UE transmits a signal with a Signal
Power level = X
4. UE adjust its
transmitting Power level
signal according to the
received TPC command
In the case of downlink CLPC mechanism the roles of the BS and the UE are
interchanged. That is, the UE compares the received signal strength from the
BS with a predefined threshold and sends the TPC to the BS to adjusts its
transmission power accordingly.
The Inner Loop is the fastest loop in WCDMA power control and hence it is
occasionally referred to as the Fast Power Control.
78
Inner Loop Power Control
The inner-loop PC relies on the feedback information at Layer I
This allows the UE/Node B to adjust its transmitted power based on the received SIR level at the Node B/UE for compensating the fading of the radio channel.
The inner-loop PC function in UMTS is used for the dedicated channels in both the UL and DL directions and for the Common Packet Channel (CPCH) in UL.
In W-CDMA fast PC with a frequency of 1.5 kHz is supported
79
Outer Loop Power Control Main target is to keep target SIR for the uplink Inner Loop Power Control in an
appreciated quality level. Due to the macro-diversity, the RNC is aware of the current radio connection conditions
and quality.
Therefore, RNC can define allowed power levels of the cell and target SIR to be used by BS when determining the TPCs.
In order to maintain the quality of the radio connection, RNC uses this power control method to adjust the target SIR and keep the variation of the quality of the connection in control.
Outer Loop Power Control fine-tunes the performance of the Inner Loop Power Control.
Signal to Interference
Ratio (SIR) (Received
SIR) caused by the UE
signal.
SIR
target
Outer Loop
Power
Control
Signal to Interference
Ratio (SIR) (Received
SIR) caused by the UE
signal.
SIR
target
Outer Loop
Power
Control
80
Outer-loop Power Control
The aim of the outer-loop PC algorithm is to maintain the quality of the communication at the level defined by the quality requirements of the bearer service in question by producing adequate target SIR for the inner-loop PC.
Done for each DCH belonging to the same RRC connection.
The frequency of outer- loop PC ranges typically from 10 to 100 Hz.
81
Throughput based CAC (TCAC)
With TCAC algorithm, admission decisions are taken based on
the capacity required by the requesting call in conjunction with current capacity usage due to ongoing connections.
The condition that needs to be met for new connection admission is that aggregate throughput in both directions of the wireless link (uplink and downlink) does not exceed certain respective maximum thresholds and therefore smooth network operation is ensured.
Given the QoS requirements of the new connection in terms of data rate and BLER as well as the applied WCDMA encoding type (e.g convolutional codes) and rate (e.g half/third rate), it is possible to compute the load increase that would occur should the connection be established using the formulas shown on next slide
82
Throughput based CAC (TCAC)
10 10
10 10
10.35 log log half rate
1.71(dB)
10.67 log log third rate
1.54
SDUb
oSDU
length BLERE
Nlength BLER
3.0
10.0
3.0
10.0
, uplink
1
10
10 , downlink
b o
b o
f
E N
UL
E N
DLf
d
W
Load increase SAF R
Rd SAF
W
where:
Eb/No Signal energy per bit divided by noise spectral density to meet predefined QoS
Length SDUThe time length of a Service Data Unit
BLER The requested BLock Error Rate for the serviced
d Downlink other-cell interference factor computed at the edge of the cell
Α Downlink spreading codes’ orthogonality factor W and WCDMA chip rate (3.84 Mcps)
R UL Requested service data rate in the uplink direction
R DL Requested service data rate in the downlink direction
SAF Service activity factor (1.0 for real-time interactive services like voice and video telephony, < 1.0 for data applications)
83
Throughput based Admission Control
In throughput-based admission control the strategy is that a new bearer is admitted only if the total load after admittance stays below the thresholds defined by the RNP.
In the UL the following equation must be fulfilled
In the DL the must be fulfilled
The UL Load Factor is obtained using
The DL Load Factor is obtained using
To obtain the load increase caused by the new user
thresholdULUL L _
thresholdDLDL L _
C
N
C
IC
I
PNIothIown
IothIown
xTotal
IothIownUL
Pr
..1
1
R
wL
max
1
Rx
RkN
j
DL
84
Wideband Power based Admission Control
The UL admission decision is based on cell-specific load thresholds given by the RNP. A RT bearer will be accepted if the non-controllable UL load, PrxNC, fulfils:
and the total received wideband interference power PrxTotal fulfils:
Power increase is obtain using
where is the uplink LF and can be obtain using
The fractional load of the new user can be calculated using
For the DL direction a similar admission algorithm is defined
etxTIxNC argPrPr
xOffsetetxTxTotal PrargPrPr
LxTotal
I
.1
Pr
xTotal
IothIownUL
Pr
..1
1
R
wL
Extra slides
85
86
UTRA Radio interface protocol layers
The radio interface of the UTRA is layered into three protocol layers: Physical Layer (L1)
Data link Layer (L2) Radio Link Control (RLC)
Medium Access Control (MAC).
Network Layer (L3).
the RLC and layer 3 protocols are partitioned in two planes, namely the User plane and the Control plane.
Control plane, Layer 3 is partitioned into sublayers where only the lowest sublayer, denoted as Radio Resource Control (RRC), terminates in the UTRAN
RRC
MAC
Layer 1
Co
ntr
ol
Co
ntr
ol
Co
ntr
ol
Mea
sure
men
ts
Mea
sure
men
ts
RRC
MAC
Layer 1
Co
ntr
ol
Co
ntr
ol
Co
ntr
ol
Mea
sure
men
ts
Mea
sure
men
ts
Measurements Report
RLC retransmission control
RLC RLC
Control Plane Control PlaneUser Plane User Plane
Radio Resource Assignment
UMTS RADIO ACCESS NETWORK USER TERMINAL
Logical Channels
Transport Channels
L3
L2
L1
PDCP PDCP
87
UTRA Radio interface protocol layers
Connections between RRC and MAC as well as RRC and L1 provide local inter-layer control services and allow the RRC to control the configuration of the lower layers.
In the MAC layer, logical channels are mapped to transport channels. A transport channel defines how traffic from logical channels is processed and sent to the physical layer.
smallest entity of traffic that can be transmitted through a transport channel is a Transport Block (TB). Once in a certain period of time, called Transmission Time Interval
(TTI), a given number of TB will be delivered to physical layer in order to introduce some coding characteristics, interleaving and rate matching to radio frame