EPL 657 Topic 7: WCDMA- Radio Resource Management · PDF fileTopic 7: WCDMA- Radio Resource...

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1 EPL 657 Topic 7: WCDMA- Radio Resource Management ΕΠΛ657 Τμήμα Πληροφορικής Πανεπιστήμιο Κύπρου

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

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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.

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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

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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.

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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

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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.

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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

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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.

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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

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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

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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.

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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.

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bit rate

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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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46

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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47

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.

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Interworking between

different functionalities and

dependancies

48

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49

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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50

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.

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Codes in UMTS/CDMA

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Overview

Access Schemes

CDMA Coding/Spreading

CDMA Codes

Code Trees

Summary of Code Characteristics

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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

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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

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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)

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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.).

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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

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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

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Heterogeneous networks and

handover (Media

Independent Handover)

59

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60

The Use Case

My Desk Undocked & walking

around

Headed out of the

building

802.3 802.11 802.16

Internet

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61

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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62

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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63

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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64

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

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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, ….

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Some preliminaries

66

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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.

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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

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Bearer services

69

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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).

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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.

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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).

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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

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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

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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.

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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.

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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.

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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

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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

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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.

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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

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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)

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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

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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

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Extra slides

85

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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

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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