LTE UE positioning in E-UTRAN

UE Positioning function is required to provide the mechanisms to support or assist the calculation of the geographical position of a UE. UE position knowledge can be used, for example, in support of Radio Resource Management functions, as well as location-based services for operators, subscribers, and third-party service providers.

Positioning functionality provides a means to determine the geographic position and/or velocity of the UE based on measuring radio signals. The position information may be requested by and reported to a client (e.g., an application) associated with the UE, or by a client within or attached to the core network. The position information is reported in standard formats, such as those for cell-based or geographical co-ordinates, together with the estimated errors (uncertainty) of the position and velocity of the UE and, if available, the positioning method (or the list of the methods) used to obtain the position estimate.

Several design options of the LTE E-UTRAN system (e.g., size of cell, adaptive antenna technique, pathloss estimation, timing accuracy, eNode B surveys) would allow the network operator to choose a suitable and cost-effective UE positioning method for their market.

Positioning the UE involves two main steps:

- signal measurements

- Position estimate and optional velocity computation based on the measurements.

The signal measurements may be made by the UE or the eNode B.

The standard positioning methods supported for E-UTRAN access are:

- network-assisted GNSS (Global Navigation Satellites Systems) methods

- downlink positioning

- enhanced cell ID method.

Hybrid positioning using multiple methods from the list of positioning methods above is also supported.

E-UTRAN UE Positioning Architecture

Above figure shows the architecture in EPS applicable to positioning of a UE with E-UTRAN access.

Location Service Support by E-UTRAN

The MME receives a request for some location service associated with a particular target UE from another entity (e.g., GMLC, eNB, or UE) or the MME itself decides to initiate some location service on behalf of a particular target UE (e.g., for an IMS emergency call from the UE). The MME then sends a location services request to an E-SMLC. The E-SMLC processes the location services request which may include transferring assistance data to the target UE to assist with UE-based and/or UE-assisted positioning and/or may include positioning of the target UE. The E-SMLC then returns the result of the location service back to the MME (e.g., a position estimate for the UE and/or an indication of any assistance data transferred to the UE). In the case of a location service requested by an entity other than the MME (e.g., UE, eNB, or E-SMLC), the MME returns the location service result to this entity.

The SLP is the SUPL entity responsible for positioning over the user plane.

source : 3GPP 3605-900

Local IP access to home based network & Internet via HNB/HeNB

3GPP specfications has specified requirements for Local IP access via femtocell access nodes ie. 3G HNB & LTE HeNB. HNB and eHNB are Customer-premises equipments (femtocell) that connect a 3GPP UE over UTRAN and EUTRAN wireless air interface respectivly to a mobile operator’s network using a broadband IP backhaul.

This is an added advantage and driver for end users to have a femtocell in home. Users would be able to access local IP devices and Internet without going through operator's network.

As per specifications Local IP Access to the home based network provides access for a directly connected (i.e. using H(e)NB radio access) IP capable UE to other IP capable devices in the home.

Further 3GPP adds that it would be possible to access Internet using local IP network also.

Traffic for local IP access is expected to not traverse the operator’s network except H(e)NB.

A logical diagram is shown below for Local IP access

A summary of requirements set by 3GPP for HNB & HeNB to support Local IP Access are as below

• Support of simultaneous access from a UE to both the operator’s core network and Local IP Access to the home based network/Internet
• Support of Local IP Access to the home based network/Internet without traversing the operator’s network except H(e)NB
• The operator or the H(e)NB Owner, within the limits set by the operator would be able to enable/disable Local IP Access to the home based network/Internet per H(e)NB.
• It would be possible to collect and make available to the operator statistics information (e.g. regular reporting of Local IP traffic volume) for each user on the use of the Local IP Access to the home based network/ Internet.
• Local IP access to home based network/ Internet would not compromise the security of the operator’s network.

Local IP access to home based network would also be possible through the H(e)NB E-UTRAN/UTRAN-interface as well however It will only be granted to UE with valid subscription.

For further readings 3GPP specification 22.220 can be referred.

Femtocell - News, Video & Whitepapers

LteWorld has recently added a new page with Femtocell news, videos & whitepapers. Page is available here.

A Femtocell is a device used to improve mobile network coverage in small areas. Femto cells connect locally to mobile phones and similar devices through their normal GSM, GPRS, or UMTS connections, and then route the connections over a broadband internet connection back to the mobile network, bypassing the normal cell towers.

Voice over LTE via Generic Access (VoLGA) Architecture

LteWorld has recently published a short tutorial about VoLGA architecture as shown below.

For more details click here.

Self-configuring and self-optimizing Networks in LTE

Self-configuring, self-optimizing wireless networks is not a new concept but as the mobile networks are evolving towards 4G LTE networks, introduction of self configuring and self optimizing mechanisms is needed to minimize operational efforts. A self optimizing function would increase network performance and quality reacting to dynamic processes in the network.

This would minimize the life cycle cost of running a network by eliminating manual configuration of equipment at the time of deployment, right through to dynamically optimizing radio network performance during operation. Ultimately it will reduce the unit cost and retail price of wireless data services.

As per 3GPP standards, a typical operational objective is to optimize the network according to coverage and capacity.

Providing optimal coverage requires that in the area, where LTE system is offered, users can establish and maintain connections with acceptable or default service quality, according to operator’s requirements. Coverage and capacity are linked, a trade-off between the two of them may also be a subject of optimization.

To achieve these objectives, 3GPP suggests to implement following functions

• Detection of unintended holes in the coverage (planned by the operator)
• Perform coverage optimization, including DL/UL channel coverage a
• Ability to balance the trade-off between coverage and capacity

Once solution is implemented, it would result in

• Continuous, optimized and matched UL and DL coverage
• Optimized DL and UL capacity of the system
• Balanced tradeoff between coverage and capacity
• Interference reduction
• Controlled cell edge performance
• Minimized human intervention in network management and optimization tasks
• Energy savings

More details about solution and use cases are available in 3GPP technical report "Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Self-configuring and self-optimizing network (SON) use cases and solutions".

Implementing self configuration and self optimization under multi vendor environment is challenging task. For this purpose, It is of importance that measurements and performance data of different vendors follow same standard. Especially when the interaction between self configuring/optimizing networks and O&M has to be considered.

Understanding CS Fallback in LTE

LTE technology supports packet based services only however 3GPP does specifies fallback for circuit switched services as well. To achieve this LTE architecture and network nodes require additional functionality, this blog is an attempt to provide overview for same.

In LTE architecture, the circuit switched (CS) fallback in EPS enables the provisioning of voice and traditional CS-domain services (e.g. CS UDI video/ SMS/ LCS/ USSD). To provide these services LTE reuses CS infrastructure when the UE is served by E UTRAN.

A CS fallback enabled terminal, connected to E UTRAN may use GERAN or UTRAN to connect to the CS domain. This function is only available in case E UTRAN coverage is overlapped by either GERAN coverage or UTRAN coverage.

The figure above provides architecture for CS fallback in EPS.

CS Fallback and IMS based services can co-exist in the same operator’s network. Although its not very straight forward to support CS fallback, all participating elements i.e UE, MME, MSC & E-UTRAN needs to support additional functionalities.

The support CS fallback in EPS a new interface SGs is added in LTE architecture. SGs interface is the reference point between the MME and MSC server. SGs interface is used for the mobility management and paging procedures between EPS and CS domain, and is based on the Gs interface procedures.

The SGs reference point is also used for the delivery of both mobile originating and mobile terminating SMS.

The CS fallback enabled network elements need to support the following additional functions:

UE

• supports access to E-UTRAN/EPC as well as access to the CS domain over GERAN and/or UTRAN.
• Combined procedures for EPS/IMSI attach, update and detach.
• CS fallback and SMS procedures for using CS domain services.

MME

• Deriving a VLR number and LAI from the GUTI received from the UE or from a default LAI.
• Maintaining of SGs association towards MSC/VLR for EPS/IMSI attached UE.
• Initiating IMSI detach at EPS detach.
• Initiating paging procedure towards eNodeB when MSC pages the UE for CS services.
• Support of SMS procedures
• Rejecting CS Fallback call request (e.g. due to O&M reasons)
• Use of the LAI and a hash value from the IMSI to determine the VLR number when multiple MSC/VLRs serve the same LAI.

MSC

• Maintaining SGs association towards MME for EPS/IMSI attached UE.
• Support of SMS procedures as provided in 3GPP specification

E-UTRAN

• Forwarding paging request and SMS to the UE.
• Directing the UE to the target CS capable cell.

At MME - MSC Server interface a new protcol SGsAP is being added to support CS fallback. SGsAP protocol is based on the BSSAP+. Stream Control Transmission Protocol (SCTP) is used to transport SGsAP signaling messages.

A CS Fallback and IMS capable UE would follow the procedures for domain selection for UE originating session/calls according to 3GPP specification 23.221.

If a UE is configured to use SMS over IP services and it is registered to IMS then it would send SMS over IMS, even if it is EPS/IMSI attached.

The home operator has option to activate/deactivate the UE configuration to use SMS over IP by means of device management in order to allow alignment with HPLMN support of SMS over IP.

When UE is performing CS fallback procedure for Mobile Originating Call for the purpose of emergency call, it needs to indicate to the MME that this CS fallback request is for emergency purpose. MME also indicates to the E-UTRAN via the appropriate S1-AP message that this CS fallback procedure is for emergency purpose.

Contents of this blog are mostly derived from 3GPP specification 23.272, for better and detailed understanding same should be referred.

Although there had been talks about another approach for CS Fallback by VoLGA which does not require any enhancement in existing CS elements like MSC but for VoLGA another set of additional nodes are needed. to know more about VoLGA refer one of our earlier blog LTE needs VoLGA.

LTE : The Global Opportunity

The UMTS Forum has came out with a report - LTE Mobile Broadband Ecosystem: the Global Opportunity. This is available for free download.

The report considers relationship in between LTE & othe mobile technologies; the new services, devices and applications which will drive LTE. Report presents a positive picture of LTE’s transformation of the global market for mobile broadband.

According to report, it is based on over 30 interviews by Ovum with operators, vendors, regulators and standards bodies, plus end user research with 550 respondents in the US, Korea, Japan, Germany, France, Italy, the UK and Spain. It considers both consumer and enterprise market segments, as well as vertical markets that will benefit from the deployment of LTE.

Report further suggests that Offering major enhancements in speed, capacity and support for new services, LTE will dominate the global market for mobile broadband over the next few years. Designed for all-IP traffic, LTE supports a flatter, more efficient network architecture that allows operators to reduce their long term capex and opex. In parallel with this, LTE allows operators to deliver a more compelling, service-rich mobile broadband user experience for consumers and business customers alike.

LTE will enhance many existing services while enabling new ones. In this new environment, non-voice mobile services – including real-time video, P2P content sharing and social networking – will be increasingly important. This evolution from a ‘traditional’ mobile ecosystem to embrace new internet-based applications, devices and content delivery mechanisms will see the emergence of a broader ecosystem than for any previous mobile technology.