voice over LTE

relay nodes

For efficient heterogeneous network planning, 3GPP LTE-Advanced has introduced concept of Relay Nodes (RNs). The Relay Nodes are low power eNodeBs that provide enhanced coverage and capacity at cell edges.  One of the main benefits of relaying is to provide extended LTE coverage in targeted areas at low cost.

The Relay Node is connected to the Donor eNB (DeNB) via radio interface, Un, a modified version of E-UTRAN air interface Uu. Donor eNB also srves its own UE as usual, in addition to sharing its radio resources for Relay Nodes.

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The Relay Node supports the eNB functionality meaning it terminates the radio protocols of the E-UTRA radio interface, and the S1 and X2 interfaces.  In addition to the eNB functionality, the RN also supports a subset of the UE functionality, e.g. physical layer, layer-2, RRC, and NAS functionality, in order to wirelessly connect to the DeNB.

With respect to the relay node’s usage of spectrum, its operation can be divided into inband and outband types.  For both inband and outband relaying, it is possible to operate the eNB-to-relay link on the same carrier frequency as eNB-to-UE links.  3GPP Release  8, UEs can connect to the donor cell in both cases.

At least "Type 1" and “Type 1a” RNs are supported by LTE-Advanced.  A "Type 1" RN is an inband RN characterized, A Type 1a relay node is characterized by the same set of features as the Type 1 relay node, except “Type 1a” operates outband.

The donor eNB  (DeNB) is enhanced to provide S1 and X2 proxy functionality between the RN and other network nodes (other eNBs, MMEs and S-GWs).  The S1 and X2 proxy functionality includes passing UE-dedicated S1 and X2 signalling messages as well as GTP data packets between the S1 and X2 interfaces associated with the RN and the S1 and X2 interfaces associated with other network nodes.  Due to the proxy functionality, the DeNB appears as an MME (for S1-MME), an eNB (for X2) and an S-GW (for S1-U) to the RN.

4G optimization and kpi analysis

The purpose is to check the performance of Network. We have categories of KPI and numbers of KPI of each category. In the Optimization process we have to check the KPI value to monitor and optimize the radio network performance in order to provide better subscriber quality or to achieve better use of installed network resources . Typically KPI can be categorized into following subcategories:'

Accessibility KPI

Are used to measure properly of whether services requested by users can be accessed in given condition, also refers to the quality of being available when users needed. eg. user request to access the network, access the voice call, data call, ......

📈 Retainability KPI

Are used to measure how the network keep user's possession or able to hold and provide the services for the users

📈 Mobility KPI

Are used to measure the performance of network which can handle the movement of users and still retain the service for the user, such as handover,...

📈 Integrity KPI

Are used to measure the character or honesty of network to its user, such as what is the throughput, latency which users were served.

📈 Availability KPI

Are used to measure the availability of network, suitable or ready for users to use services.

📈 Utilization KPI

Are used to measure the utilization of network, whether the network capacity is reached its resource.

KPIs for LTE RAN (Radio Access Network)

LTE KPI	INDICATORS
Accessibility KPI	RRC setup success rate ERAB setup success rate Call Setup Success Rate Are used to measure properly of whether services requested by users can be accessed in given condition, also refers to the quality of being available when users needed. eg. user request to access the network, access the voice call, data call, ......
Retainability KPI	Call drop rate Service Call drop rate Are used to measure how the network keep user's possession or able to hold and provide the services for the users
Mobility KPI	Intra-Frequency Handover Out Success Rate Inter-Frequency Handover Out Success Rate Inter-RAT Handover Out Success Rate (LTE to WCDMA) Are used to measure the performance of network which can handle the movement of users and still retain the service for the user, such as handover,...
Integrity KPI	E-UTRAN IP Throughput IP Throughput in DL E-UTRAN IP Latency Are used to measure the character or honesty of network to its user, such as what is the throughput, latency which users were served.
Availability KPI	E-UTRAN Cell Availability Partial cell availability (node restarts excluded) Are used to measure how the network keep user's possession or able to hold and provide the services for the users
Utilization KPI	Mean Active Dedicated EPS Bearer Utilization Are used to measure the utilization of network, whether the network capacity is reached its resource.

 

ACCESSIBILITY KPI:

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☰ RRC Setup Success Rate

RRC setup success rate is calculated based on the counter at the eNodeB when the eNodeB received the RRC connection request from UE. Number of RRC connection attempt is collected by the eNodeB to the measurement at point A, and the number of successful RRC connection calculated at point C. Here's an illustration:

 

☰ ERAB setup success rate

ERAB setup success rate KPI shows the probability of success ERAB to access all services including VoIP in a cell or radio network. KPI is calculated based counter ERAB connection setup attempt (point A) and successful ERAB setup (point B). The explanation is as given in the following illustration:

☰ Call Setup Success Rate

Call Setup Success Rate KPI call setup indicates the probability of success for all service on the cell or radio network. KPI is calculated by multiplying the RRC setup success rate KPI, S1 signaling connection success rate KPI, and ERAB success rate KPI. The table below describes the definition Call Setup Success Rate:

 

RETAIN-ABILITY KPI:

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☰ Call Drop

VoIP call drop arise when VoIP ERAB release is not normal. Each ERAB associated with QoS information. Here's an illustration of two procedures being done to release ERAB namely: ERAB release indication and the UE context release request:

MOBILITY KPI:

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☰ Intra-Frequency Handover Out Success Rate

Intra-Frequency Handover Success Rate Our KPI shows intra-frequency handover success rate of locall cell or radio network to the intra-frequency neighboring cell or radio network. Intra-frequency HO included in a single cell eNodeB or different eNodeB.
Intra-frequency HO scenario shown in the figure below:

No attempt HO calculations at point B. When ENodeB sending RRC connection reconfiguration message to the EU, he will do the handover. ENodeB will count the number of times the HO attempt at the source cell. HO calculation of success is at point C. The HO ENodeB count the number of the source cell when ENodeB receive RRC connection reconfiguration message complete of the EU.
Here's a scenario intra-frequency handovers inter ENodeB:

Handover attempt occurs at point B, when the source ENodeB (S-eNodeB) sends RRC connection reconfiguration message to the UE. He decided to conduct inter ENodeB HO. in this KPI, the source and the target cell work on the same frequency. The number of the attempt HO calculated at the source cell. The number of successful HO occurs at point C. During HO, HO amount which success is measured in the cell souce. This measurement appears typing S-eNodeB received a UE context release message from the target eNode B (T-eNodeB), or the UE context release command from the MME, which shows that the UE-eNodeB T has successfully attach at the T-eNodeB.
The following scenarios illustrate intra frequency B HO - inter ENodeB:

Following the definition of Intra Frequency Out Handover Success Rate KPI:

☰ Inter-RAT Handover Out Success Rate (LTE to WCDMA)

Inter RAT Handover Out Success rate shows the success rate KPI HO from LTE cell or radio network to a WCDMA cell.
Here's a scenario out inter RAT handover success rate:

Inter RAT handover success rate out

INTEGRITY KPI:

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☰ E-UTRAN IP Throughput

A KPI that shows how E-UTRAN impacts the service quality provided to an end-user.
Payload data volume on IP level per elapsed time unit on the Uu interface. IP Throughput for a single QCI:

To achieve a throughput measurement that is independent of bursty traffic pattern, it is important to make sure that idle gaps between incoming data is not included in the measurements. That shall be done as considering each burst of data as one sample. ThpVolDl is the volume on IP level and the ThpTimeDl is the time elapsed on Uu for transmission of the volume included in ThpVolDl.

☰ E-UTRAN IP Latency

A measurement that shows how E-UTRAN impacts on the delay experienced by an end-user.
Time from reception of IP packet to transmission of first packet over the Uu.
To achieve a delay measurement that is independent of IP data block size only the first packet sent to Uu is measured.
To find the delay for a certain packet size the IP Throughput measure can be used together with IP Latency (after the first block on the Uu, the remaining time of the packet can be calculated with the IP Throughput measure). 

T_Lat is defined as the time between receiption of IP packet and the time when the eNodeB transmits the first block to Uu.
Since services can be mapped towards different kind of E-RABs, the Latency measure shall be available per QoS group.

AVAILABILITY KPI:

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☰ E-UTRAN Cell Availability

E-UTRAN Cell Availability.
A KPI that shows Availability of E-UTRAN Cell.
Percentage of time that the cell is considered available.

As for defining the cell as available, it shall be considered available when the eNodeB can provide E-RAB service in the cell.

UTILIZATION KPI:

 

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☰ Mean Active Dedicated EPS Bearer Utilization

This KPI describes the ratio of the mean number of active dedicated EPS bearer to the maximum number of active dedicated EPS bearers provided by EPC network, and it is used to evaluate utilization performance of EPC network.
This KPI is obtained by the mean number of dedicated EPS bearers in active mode divided by the system capacity.

The mean number of simultaneous online and answered sessions together with maximum number of sessions provided by network can reflect system resource utilization. If the value of this KPI is very high, it indicates system capacity is not enough, and needs to be increased. This KPI is focusing on network view.

eUTRAN parameters and planning

eUTRAN Parameters Description and Planning

Basic Cell Parameter: ECGI Planning 

• ECGI = PLMN + Cell Identity 
• PLMN = MCC + MNC 
• Cell Identity = eNodeB ID + Cell ID 
• Parameter Description 
• ECGI : It indicates the E-UTRAN cell global identifier. 
• MCC: It indicates the country code of the mobile subscriber. 
• MNC: Its indicates the code of network used by the mobile subscriber. 
• Cell Identity: It is of 28 bits. The former 20 bits indicate the eNodeB ID, and the latter 8 bits indicate the cell ID.

Basic Cell Parameter: ECGI Planning 

1. MCC: It is of 3 bits. Its value ranges from 0 to 999.

2. MNC: It is of 2 bits or 3 bits. Its value ranges from 0 to 999.

3. eNodeB ID: Its value ranges from 0 to 1048575. The eNodeB ID is unique to every eNodeB in the same PLMN. When you are planning the eNodeB ID, you need to take the network scale into account. Generally speaking, there is small-sized network, standard-sized network, large-sized network and shared network.
4. Cell ID: It is unique to every cell in the same eNodeB. Its value ranges from 0 to 255.

Basic Cell Parameter: eNodeB ID

1. Standard-Sized Network

The eNodeB ID appears to be ABCDEF in a standard-sized network.
The first two figures (namely AB) indicate the city where the eNodeB is located.
The last figure (namely F) indicates whether it is an indoor eNodeB or an outdoor eNodeB. If the last figure appears to be “0”, it is an indoor eNodeB. Otherwise, it is an outdoor eNodeB. 

 2. Large-Sized Network
In most cases, the eNodeB ID appears to be ABCDEF.
The first two figures (namely AB) indicate the city where the eNodeB is located.
Different AB combination indicates different cities. The AB combination can indicate at most 90 cities, each of which can hold 9999 eNodeBs at most. Sometimes, the network may cover more than 90 cities. In this case, use every AB combination to indicate two or more than two cities. Each city can hole at most 5000 eNodeBs.
The last figure (namely F) indicates whether it is an indoor eNodeB or an outdoor eNodeB. If the last figure appears to be “0”, it is an indoor eNodeB. Otherwise, it is an outdoor eNodeB.
In some special cases, if F appears to be “9”, it is a remote eNodeB.
3. Shared Network If it is a shared network, for example the TDD-FDD network in Hi3G project, you will use 6-digit eNodeB ID (ABCDEF).
The first figure (namely A) indicates the network schema. “1” stands for the TDD network, and “5” stands for the FDD network.
The second figure (namely B) indicates the city where the eNodeB is located.
The third figure (namely C) may indicate the administrative region where the eNodeB is located.
The last figure (namely F) indicates whether it is an indoor eNodeB or an outdoor eNodeB. If the last figure appears to be “0”, it is an indoor eNodeB. Otherwise, it is an outdoor eNodeB

Basic Cell Parameter: CP

• CP Selection for Physical Channel 
• Parameter Description 
• This parameter indications the cyclic prefix(CP) of the OFDM symbol,which is used to determine the total number of OFDM symbols within one slot. When this parameter is set to normal cyclic prefix, it implies that seven OFDM symbols are available within one slot. When this parameter is set to extended cyclic prefix, it implies that six OFDM symbol are available within one slot. 
• Value Range and Step Length 
• Value Range: enum (normal cyclic prefix, extended cyclic prefix) 
• Default Value: normal cyclic prefix 
• Configuration Principles 
• The cp is dependent on the multipath delay of a radio channel. In the presence of either a large mutipath delay or a large cell radius, extended cyclic prefix is recommended. 
• The extended cyclic prefix option can suppress radio interference caused by multipath delay, but suffering from lower system capacity, and therefor it is recommended that you set it to the default value.

Basic Cell Parameter: Bandwidth

• Downlink System Bandwidth 
• Parameter Description 
• This parameter indicates the system bandwidth in the downlink, which is used to determine the frequency domain location of the downlink physical channel as well as downlink frequency allocation. 
• Value Range and Step Length 
• Value Range: enum (6, 15, 25, 50, 75, 100) Unit RB 
• Default Value: 100 
• Configuration Principles 
• This parameter is dependent on the frequency bandwidth acquired by a mobile operator. The downlink system bandwidth can either be identical to or different from the uplink system bandwidth. 
• Modifying this parameter can have an impact on downlink resource allocation
• Uplink System Bandwidth 
• Parameter Description 
• This parameter indicates the system bandwidth in the uplink , which is used to determine the frequency domain location of the uplink physical channel as well as uplink frequency allocation. 
• Value Range and Step Length 
• Value Range: enum (6, 15, 25, 50, 75, 100) Unit RB 
• Default Value: 100 
• Configuration Principles 
• This parameter is dependent on the frequency bandwidth acquired by a mobile operator. The system uplink bandwidth can either be identical to or different from the downlink system bandwidth. 
• Modifying this parameter can have an impact on uplink resource allocation

Basic Cell Parameter: Transmit Power 

• Cell Max Transmit Power 
• lParameter Description 
• This parameter specifies the maximum available transmit power. 
• Value Range and Step Length 
• Value Range: float (0, …, 50) step 0.1 Unit dBm 
• Default Value: 43 
• Configuration Principles 
• The default value is intended to be used in the following environment:

Basic Cell Parameter: Transmit Power 

• Cell Transmit Power 
• lParameter Description 
• This parameter specifies the used transmit power. 
• Value Range and Step Length 
• Value Range: float (0, …, 50) step 0.1 Unit dBm 
• Default Value: 43 
• Configuration Principles 
• For the environment information about the use of the default value, see page 13(Cell Max Transmit Power). 
• This parameter is dependent on the cell radius and the planned downlink throughput at the cell edge. The greater the cell radius or the planned downlink throughput at the cell edge, the greater the value of this parameter is required.
• Cell-specific Reference Signals Power 
• Parameter Description 
• This parameter specifies the absolute power value of the cell reference signal for each resource element. 
• Value Range and Step Length 
• Value Range: int (-60, …, 50) Unit dBm 
• Default Value: 6 
• Configuration Principles 
• This parameter is dependent on cell coverage. The greater the cell coverage, the greater the value of this parameter is required. This parameter should be used for ensuring cell coverage while achieving the maximum power. 
• A reference signal power value should be properly tuned in accordance with the required power of the downlink control channel at the cell edge based on the link estimation calculated by using such radio parameters as cell type ,cell radius, and antenna height.

Part 2 Tracing Area Planning

Tracing Area Planning : Paging Process

• The idle UE can monitor the paging message by means of discontinuous reception (DRX). It detects whether the PDCCH carries the P-RNTI on the paging occasion of specified paging frame. The detection results will tell the UE whether this PDSCH carries paging message. 
• a) If the PDCCH carries the P-RNTI, the UE receives the data from the PDSCH based on the PDSCH parameters. 
• b) If the PDCCH does not carry the P-RNTI, the UE changes into the dormant status. 
• Within a DRX period, the UE can receive the PDCCH data when the paging occasion appears, and then receive the PDSCH data based on the actual requirements. 
• As specified by the LTE physical layer protocol, the radio frame No. repetition period is 1024. Every radio frame is divided into ten sub-frames. In this regard, if the UE wants to know the accurate location of the PDCCH to be monitored, it needs to work out the radio frame No. for this PDCCH, and then work out the paging occasion (PO) for this radio frame number. 

Tracing Area Planning : Paging Parameters

• DRX Cycle for Paging 
• Parameter description 
• This parameter specifies the DRX cycle for paging purposes. 
• Value Range and Step Length 
• Value Range: enum (32, 64, 128, 256) Unit; subframe 
• Default Value:128 
• Configuration Principles 
• When the UE is in idle state but the DRX is being used, the UE needs to monitor a P-RNTI in a paging occasion every DRX cycle. 
• Modifying this parameter can have an impact on other UEs being in idle state.
• nB used to derive the Paging Frame and Paging Occasion 
• Parameter description 
• nB is used to derive the paging frame and paging occasion, as defined in TS36.304 
• Value Range and Step Length 
• Value Range: enum (4T, 2T, T, 1/2T, 1/4T, 1/8T, 1/16T, 1/32T) 
• Default Value:T 
• Configuration Principles 
• T represents a paging cycle. For example 2T indicates two default paging cycles. 
• It indicates the paging attempts made by a radio frame. Its value can be 4T
• The Parameter to Detemine BCCH Modification Period 
• Parameter description 
• This parameter is used to determine the BCCH modfication period(BCCH modification period=N*DRX cycle length for paging).The purpose of this constraint is to ensure that all the UEs being in idle state can monitor the system broadcast change message. 
• Value Range and Step Length 
• Value Range: enum (2,4,8,16) 
• Default Value:4 
• Configuration Principles 
• The greater this parameter, the longer the system message is updated.This can have a adverse impact on real-time message update. 
• The smaller this parameter, the shorter the system message is updated. This can cause the UE to monitor the system Info Value Tag more frequently

Tracing Area Planning 

• TAC: It indicates a tracing area in a PLMN. It is used to manage the UE location and find the desired UE. 
• 1. The TAC is unique in a PLMN. 
• 2. A cell must belong to a tracing area (TA) exclusively. When you configure the TAC, you need to consider the quantity of cells in this TA. 
• 3. The bonding relation between the TAC and the cell is determined by the cell size, cell type (high-speed cell or low-speed cell) and TA list configuration.
• Principles 
• 1.Determine the size of tracing area based on the UE paging capability and the network . 
• 2.Avoid frequent IRAT cell re-selection and LAU/TAU. 
• 3.Take the geographical features into account. 
• a) Do not place the tracing area boundary in the heavy-traffic area (e.g. downtown area, or central business district). Place the boundary in the low-traffic area (e.g. suburban area, or factories). 
• b) The tracing area boundary should be orthogonal or diagonal to the road. Moreover, keep the overlapped part between tracing areas away from the area where UE moves in high speed. 
• c) Do not place different tracing area boundaries in the same small area. Otherwise, the UE may frequently update the tracing area information or perform handovers between these tracing areas. 
• 4.Take the traffic increase tendency into account so as to provide tracing areas with proper paging capacity, traffic capacity and expandability of the tracing area.

Part 3 PCI Planning

PCI Planning (1)

PCI Planning (2)

• Principles 
• 1）If there are cell A, cell B and cell C, the cell A and the cell B make up a group of neighboring cells while the cell B and cell C make up another group of neighboring cells, then the cell A and the cell C must use different PCIs. 
• 2）When you allocating PCIs to different cells controlled by the same eNodeB, all these PCIs should comply with the mod3 principle. Additionally, consider the mod3 principle when you allocating the PCI to the cell and its nearest neighboring cell. 
• 3）Cells sharing the same PCI should be far from each other as much as possible.

Part 4 PRACH Planning

Random Access Parameter

1.Cell High-speed Attribute
2.Ncs Used to Generate PRACH Preamble
3.Logical Root Sequence Start Number Used to Generate PRACH Preamble
4.Number of Non-dedicated Random Access Preambles
5.Size of Random Access Preambles Group
6.Threshold of Selecting Preamble Group
7.Message Power Offset for Group B
8.the Initial RB Number for Random Access Preambles
9.PRACH Configuration Index
10.Initial Power for Preamble of PRACH
11.Power Ramping Step for PRACH
12.Max retransmit number for PRACH
13.TTI Window Size for PRACH Response
14.Max Number of Messages HARQ Transmissions
15.MAC Contention Resolution Timer
16.Dedicated Preamble Life Time 

Physical Random Access Channel (PRACH) is mainly used during the random access process.
The functions of random access in LTE include the following:

-Obtaining UL synchronization during initial access and handovers.
-Assigning a unique C-RNTI for the UE during initial network access establishment.

An example
is when the status is changed from RRC_IDLE to RRC_CONNECTED.
Two scenarios are involved in the random access process:
Scenario I: Contention-Based Access
Scenario II: Contention-Free Access

There are two types of random access: 

• Synchronized Random Access 
• Non-synchronized Random Access 

The random access is performed in two modes: 

• Contention-based access (The UE selects a random preamble) 
• Contention-free access (The eNodeB assigns a dedicated preamble to the UE.) 

Triggers for Initial Access and Random Access 

• RRC_IDLE (initial access) 
• Break of radio link (initial access) 
• Handover (random access) 
• RRC_CONNECTED, the downlink data is arriving but the uplink is out-of-synchronization. (random access) 
• RRC_CONNECTED, the uplink data is arriving but the uplink is out-of-synchronization, or the scheduling request is received from the PUCCH (random access) 

Contention –based Access: applicable to all these five triggers
Contention-free Access: applicable to No.3 and No.4 triggers. 

• PRACH Format Selection 
• Considering the resources occupied by the PRACH, and the 
• coverage area and features of macro cells, please select format 0 
• when configuring the initial network. 
• PRACH Root μ Sequence Selection Principles: 
• (1) The root μ sequences between neighboring cells should be different. 
• (2) The distance between cells whose root μ sequence should meet requirements. 
• (3) Select the root μ sequence with smaller cyclic shift for the high speed scenario. 
• The Ncs in the high speed scenario should be proper so as to address the impact left to the peak data rate check from the cyclic shifting caused by frequency offset. 
• The recommended value is given in the protocol.

Part 5 Neighboring Cell Planning

Neighboring Cell Planning 

• The neighboring cell planning aims to ensure voice quality and performance of the entire network as the UEs on the cell edge can be handed over to their neighboring cells with the best signals. 
• The principles are as follows: 
• 1.Normally, the geographically adjacent cells are configured as neighboring cells; 
• 2.Oftentimes, the neighboring cell relation is bilateral; at times, the neighboring cell relation is unilateral; 
• 3.The number of neighboring cells should be proper. That is, either excessive or few neighboring cells are improper. With excessive neighboring cells, the UE measurement might be overloaded; with few neighboring cells, evitable call drops and handover failures might occur without neighboring cells. At most 16 neighboring cells are recommended for initial configuration. 
• 4.The neighboring cell planning should be based on the drive test and actual radio environment. For suburban and rural areas, to ensure possible handovers, neighboring cells should be configured even if the inter-site distance is long.

Part 6 Frequency Planning

• Usually, the entire LTE network adopts the same frequency band. For example, 20 MHz bandwidth is used for the entire network. To avoid ICIC, you need to allocate different bands for different cells. Ensure that two cells with great overlapped coverage should better not use the same frequency resources. 
• Currently, frequency allocation includes four modes: 
• Based On Same-Frequency 
• Based on SFR(Non Exclusive IC) 
• Based on SFR(Exclusive IC) 
• Based on Differ-Frequency

Static ICIC Realization

• Static SFR 
• As shown in the left figure, the whole frequency band is divided into three equal part. f1, f2 and f3 indicate the outer cell of three sectors.

• Static FFR 
• As shown in the right figure, the whole frequency band is divided into four parts. It is similar to the case that the f1 in SFR mode is divided into three equal parts, each of which serves as the outer cell area of three sectors. In this way, cell edge users (CEUs) are separated from cell center users (CCUs), reducing the interference from the side lobe users in the neighboring cell to the CCUs of the service cell.