3gLteInfo

Why Operators Need Self Organizing Network(SON)?

Prashant Panigrahi — Mon, 25 Feb 2013 12:51:04 +0000

Self Organizing Network helps in reducing the system overload in an automated way. This new video from Ericsson describes what is SON and how Self Organizing Network will help not only LTE but also in older technologies like 3G and 2G. Automation creates value within the network and self organizing networks are increasingly important not only to lower costs of deployment and operations, but also to offer a better user experience.

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Mobile Phones Journey in Last 31 Years

3gLteInfo — Tue, 19 Feb 2013 15:36:47 +0000

Mobile phones had a long history. The last three decades of mobile phones is quite amazing. Check out this infographic.

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Voice Over LTE – VoLTE Signalling Call Flow

Prashant Panigrahi — Fri, 25 Jan 2013 10:49:57 +0000

Voice over LTE – VoLTE is the technology to provide voice and video services over LTE all PS network. As LTE is a complete PS network VoLTE need to use IMS in EPS core to handle voice and video related services. Apart from IMS, VoLTE enabled UE (User Equipment) use MME (Mobility Management Entity) to authenticate a UE prior to entering the EPC. MME need to communicate with HSS which in turn communicate with AAA server for authentication, authorization and accounting purposes.

After authentication procedure is over a control signalling is used to create a default bearer to internet. MME then select the appropriate SGW (Serving Gateway) to connect to eNodeB.

SIP is the most important protocol in VoLTE communication. It is in charge of all signalling required to setup, manage and terminate the session. UDP (User Datagram Protocol ) protocol is used for transmission of actual VoLTE user data packets.

This LTE video tutorial describes:

Authentication of UE in VoLTE call
How control signalling is used to create default bearer in VoLTE
How default internet bearer is established
Control signalling to create default IMS bearer.
Default IMS bearer establishment.
IMS registration via SIP
Notify change of state
Actual VoLTE call data packet transmission on UDP

VoLTE Signalling Call Flow – Video Tutorial

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Multi-Carrier Heterogenous Networks (HetNet) Performance

3gLteInfo — Tue, 22 Jan 2013 12:44:23 +0000

Heterogeneous networks (HetNets), consisting of Macro NodeBs (macros) and low power Pico NodeBs (picos), can increase system capacity by offloading some users to the picos. However, this offloading may be limited due to intercell interference from macros to picos that reduces their coverage. HSPA Multi-carrier HetNets allow the use of range expansion techniques to achieve more offloading, such as power reduction from the macros on one carrier. “Performance Analysis of HSPA Multi-Carrier Heterogenous Networks” white paper provides a system level analysis of the gain provided by power reduction on one carrier of the macros in a HetNet environment. As the interference from the macros is reduced, more capacity offloading to picos occurs and higher system capacity can be achieved. By considering cell biasing in serving cell selection, further gains can be observed.

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VoLTE Battery Issue and Solution from ST Ericsson

Prashant Panigrahi — Mon, 14 Jan 2013 12:27:45 +0000

VoLTE was in bad limelight because of it’s battery performance issues. I wrote an article how VoLTE will consume twice battery than traditional voice calls. The study was done by Metrico Wireless using LG Connect 4G on MetroPCS network.

ST Ericsson provided a new white paper which clarifies all doubts around VoLTE. Without VoLTE CDMA/LTE systems suffer a severe penalty in that they use a concept called Simultaneous Voice and LTE – SVLTE. This means that during a voice call, both the CDMA radio and the LTE radio are in full operation. The consequence of this is clearly visible in the Metrico data, which also shows the obvious fact that VoLTE+LTE consume less power than CDMA+LTE.

But LTE Networks with 3GPP based legacy systems like UMTS and GSM does not suffer from these issue. Also CDMA + LTE solutions based on fall-back schemes do not have this problem.

ST Ericsson provided many way to tackle this issue using better software architecture, optimizing radio hardware and transmission protocols.

What do you think about these solutions? Will these really help in solving battery issue in VoLTE?

Here is the the ST Ericsson white paper on VoLTE battery problem and solution for the problem.

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Carrier Aggregation in LTE Advanced

Prashant Panigrahi — Fri, 11 Jan 2013 14:52:01 +0000

What is carrier aggregation and how this will help in improving bandwidth and throughput?

ITU set specific requirements for IMT Advanced compliant technology should fulfill. Some of these requirements include at least 40 MHz bandwidth, peak spectral efficiency of 15 bit/s/Hz in downlink and 6.75 bit/s/Hz in uplink and control plane and user plane latency of less than 100 and 10 ms respectively. Carrier aggregation is supported for both FDD and TDD.

Carrier aggregation is a LTE Advanced feature to increase aggregate bandwidth in order to improve data throughput in 4G mobile communication systems. Carrier aggregation in LTE was first introduced in 3GPP release 10 and further improvements are ongoing in Release 11 and onward. To make carrier aggregation backward compatible carriers used in this new feature are R8/R9 carriers.

A Rel-10 UE with reception and/or transmission capabilities for CA can simultaneously receive and/or transmit on multiple Component Carriers (CCs) corresponding to multiple serving cells.
A Rel-8/9 UE can receive on a single Component Carrier and transmit on a single Component Carrier corresponding to one serving cell only.

Carrier Aggregation is supported for both contiguous and non-contiguous Component Carriers with each Component Carrier limited to a maximum of 110 Resource Blocks in the frequency domain using the Rel-8/9 numerology.

The number of DL Component Carriers that can be configured depends on the DL aggregation capability of the UE.
The number of UL Component Carriers that can be configured depends on the UL aggregation capability of the UE.
It is not possible to configure a UE with more UL Component Carriers than DL Component Carriers.
In typical TDD deployments, the number of Component Carriers and the bandwidth of each Component Carrier in UL and DL is the same.

The spacing between centre frequencies of contiguously aggregated CCs shall be a multiple of 300 kHz. This is in order to be compatible with the 100 kHz frequency raster of Rel-8/9 and at the same time preserve orthogonality of the subcarriers with 15 kHz spacing.

Carrier Aggregation in Layer 2

In case of Carrier Aggregation the multi-carrier nature of the physical layer is only exposed to the MAC layer for which one HARQ entity is required per serving cell.

In both uplink and downlink, there is one independent hybrid-ARQ entity per serving cell and one transport block is generated per TTI per serving cell in the absence of spatial multiplexing. Each transport block and its potential HARQ retransmissions are mapped to a single serving cell.

The reception timing difference at the physical layer of DL assignments and UL grants for the same TTI but from different serving cells (e.g. depending on number of control symbols, propagation and deployment scenario) does not affect MAC operation. A UE should cope with a relative propagation delay difference up to 30 microseconds among the component carriers to be aggregated in inter-band non-contiguous CA. This implies that a UE should cope with a delay spread of up to 31.3 micro seconds among the component carriers monitored at the receiver, since the BS time alignment is specified to be up to 1.3 microseconds.

Layer 2 Structure for downlink with CA configured

Layer 2 Structure for uplink with CA configured

RRC Carrier Aggregation

When CA is configured, the UE only has one RRC connection with the network. At RRC connection establishment/reestablishment/handover, one serving cell provides the NAS mobility information (e.g. TAI), and at RRC connection reestablishment/handover, one serving cell provides the security input. This cell is referred to as the Primary Cell (PCell).

In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC).

Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC).

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LTE Logical Channels

Prashant Panigrahi — Fri, 11 Jan 2013 10:33:18 +0000

LTE logical channels structure and mapping between logical channels and transport channels.

Logical channels reside between RLC sublayer and MAC sublayer which are layer 2 protocols in LTE protocol stack. Logical channels tells what kind of information is transferred. Logical channels can be broadly divided into two types:

Control Channels (for the transfer of control plane information)
Traffic Channels (for the transfer of user plane information)

Control Channels

Control channels are use for transferring control plane information. The different control channels in LTE are:

Broadcast Control Channel (BCCH)

BCCH channel is used for transferring system control information. Broadcast Control Channel (BCCH) is a downlink channel.

Paging Control Channel (PCCH)

PCCH is a downlink channel which carries paging information and system information change.

Common Control Channel (CCCH)

Channel for transmitting control information between UEs and network. This channel is used for UEs having no RRC connection with the network.

Multicast Control Channel (MCCH)

A point-to-multipoint downlink channel used for transmitting MBMS control information from the network to the UE, for one or several MTCHs. This channel is only used by UEs that receive or are interested to receive MBMS.

Dedicated Control Channel (DCCH)

DCCH is used when there is RRC Connection. DCCH transfers dedicated control information between UE and network. Dedicated Control Channel (DCCH) is a bidirectional channel.

Traffic Channels

Traffic channels are used to carry user plane information. There are two types of logical traffic channels available in LTE

Dedicated Traffic Channel (DTCH)

DTCH is a bi-directional channel used to transfer user plane information between UE and network.

Multicast Traffic Channel (MTCH)

A point-to-multipoint downlink channel for transmitting traffic data from the network to the UE. This channel is only used by UEs that receive MBMS.

Mapping between logical channels and transport channels

Mapping in uplink

Mapping in downlink

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