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.

UMTS/LTE in 800 MHz for Europe

800MHz band (also known as 790-862 MHz, channels 61 to 69 in UHF Bands IV and V) was previously used by analog broadcasting, and is particularly suitable for delivery of high-bandwidth services and indoor coverage.

UK regulator Ofcom is pushing to clear the 800MHz band of existing and previously planned users and align the upper band of the UK’s digital dividend with the spectrum being identified for release by an increasing number of other European countries. The reason behind this move is that this spectrum is likely to be particularly suitable for the provision of a new generation of mobile broadband services.

A 3GPP work item is currently under works to provide specification for "UMTS/LTE in 800 MHz for Europe" to provide support for LTE and UMTS with paired channel arrangement in the band 790-862 MHz.

Based on 3GPP work item the 790-862 MHz band is arranged as 2x30 MHz with 11 MHz duplex gap:

• FDD Uplink: 832 – 862 MHz
• FDD Downlink: 791 – 821 MHz

The tasks identified by 3GPP in this work item includes, study of UMTS/LTE in upper UHF band for a potential deployment in ITU Region 1, generate a new technical report based on study results and develop channel arrangement in line with the pending ECC decision.

The target date set by the EC for analog switch-off in EU member countries is 2012. Finland, Sweden, France, Switzerland, Germany, Spain and Denmark have already decided to release the whole of the 800 MHz band, with others likely to follow. More speed is both necessary and desirable to fully realize the benefits.

The State of 3G and LTE in India

With wireless subscription having reached to 441.66 Million, India has yet to catchup with other countries in 3G and LTE (Long Term Evolution) deployments. India's state-run mobile operators BSNL and MTNL have already launched commercial 3G services after getting access to spectrum last year. BSNL and MTNL have set sights on adding between 200,000 and 300,000 subscribers during the first year of operations.

DoT and finance ministry recently indicated to limit the number of slots to just four blocks of 5 MHz each in the 2.1 GHz band for 3G auctions with a view to maximizing revenue per block of spectrum. These four new entrants will be in addition to BSNL/MTNL, taking the total 3G operators per circle to five.

Even as the policy for auctioning spectrum for 3G mobile services is yet to be finalized, the Department of Telecom is already thinking about the introduction of 4G technologies such as LTE. It says some spectrum must be retained to accommodate the future needs of these operators as well as to provide for 4G technology (LTE) which will require a minimum channel of 10 MHz for the launch of service.

However telecom operators RCOM, Tata, Systema and equipment vendor Qualcomm strongly are opposing the government’s move to restrict 3G spectrum auctions to four blocks per circle. These companies want all spectrum to be put on the block so that the demand-supply equation pushes down its price.

The final decisions will be made by Empowered Group of Ministers (EGoM) in the next few weeks, based on which 3G auctions are expected either by early December or after January 2010.

It is still not clear how many operators could get 3G & LTE spectrum. Similar to 3G, LTE may come in India in 2.1 Ghz band, as 2.5 Ghz (EU LTE spectrum) is mostly used for satellite-based networks. In India most operators are looking to move to this technology by 2011, once they start making money on 3G services. MTNL & BSNL may again lead LTE deployments.

LTE Advanced: Evolution of LTE

LTE standards are in matured state now with release 8 frozen. While LTE Advanced is still under works. Often the LTE standard is seen as 4G standard which is not true. 3.9G is more acceptable for LTE. So why it is not 4G? Answer is quite simple - LTE does not fulfill all requirements of ITU 4G definition.

Brief History of LTE Advanced: The ITU has introduced the term IMT Advanced to identify mobile systems whose capabilities go beyond those of IMT 2000. The IMT Advanced systems shall provide best-in-class performance attributes such as peak and sustained data rates and corresponding spectral efficiencies, capacity, latency, overall network complexity and quality-of-service management. The new capabilities of these IMT-Advanced systems are envisaged to handle a wide range of supported data rates with target peak data rates of up to approximately 100 Mbit/s for high mobility and up to approximately 1 Gbit/s for low mobility.

In order to meet this new challenge, 3GPP widened its scope to include systems beyond 3G. LTE Advanced would fulfil the 4G requirements as set by ITU. In 2008 3GPP held workshops on IMT Advanced, where the “Requirements for Further Advancements for E-UTRA” were gathered. The resulting Technical Report 36.913 has been now published.

Let us see some requirements which differentiate LTE & LTE Advanced.

Peak data rate:

• LTE - DL: 100 Mbps, UL: 50 Mbps
• LTE Advanced - DL: 1 Gbps, UL: 500 Mbps

Transmission bandwidth:

• In comparison to LTE, LTE Advanced is wider than approximately 70 MHz in DL and 40 MHz in UL.

Latency:

• LTE - C-plane from Idle (with IP address allocated) to Connected in <100>
• LTE Advanced - C-plane from Idle (with IP address allocated) to Connected in <50>

Peak spectrum efficiency:

• LTE - DL 3 to 4 times Release 6 HSDPA , UL - 2 to 3 times Release 6 Enhanced Uplink
• LTE Advanced - DL 30 bps/Hz and UL 15 bps/Hz.

C-plane capacity:

• LTE - At least 200 users per cell should be supported in the active state for spectrum allocations up to 5 MHz.
• LTE Advanced - At least 300 active users without DRX in a 5 MHz bandwidth.

Mobility:

• LTE - Support mobility across the cellular network for various mobile speeds up to 350km/h (or perhaps even up to 500km/h depending on the frequency band).
• LTE Advanced - Same as that in LTE, System performance shall be enhanced for 0 to 10km/h

LTE Advanced would operate in spectrum allocations of different sizes including wider spectrum allocations than those of Release 8 to achieve higher performance and the target peak data rate, e.g. up to 100 MHz.