LTE Interfaces and Protocols


The main interfaces in LTE are Uu, S1-MME, X2, S1-U, S11 and S5.

LTE Uu: -
This is the air interface between UE and eNB. LTE layer 1 is dealt with later. RRC is the protocol that is used for communication between UE and eNB. Above RRC there is a NAS layer in UE. This NAS layer terminates at MME and eNB shall silently pass the NAS messages to MME.

LTE S1-MME: -
eNB and MME communicate using this IP interface. S1-AP is application layer interface. The transport protocols used here is SCTP. (Stream control transmission protocol)

LTE X2: -
This interface is used by a eNB to communicate to other eNB. This again is a IP interface with SCTP as transport. X2-AP is the application protocol used by eNB’s to communicate.

LTE S11: -
An IP interface between MME and SGW! GTPv2 is the protocols used at the application layer. GTPv2 runs on UDP transport. This interface must and should run GTPv2.
LTE S5: -
This is the interface between SGW and PGW. This again is an IP interface and has two variants. S5 can be a GTP interface or PMIP interface. PMIP variant is used to support non-trusted 3GPP network access.
LTE S1-U: -
User plane interface between eNB and SGW! GTP-U v1 is the application protocol that encapsulates the UE payload. GTP-U runs on UDP.

All the above IP interfaces can be of IPv4 or IPv6. Few interfaces can be of IPv4 and few can be of IPv6. From the specification side there are no restrictions.

LTE Idle Mode – Cell Reselection


After cell selection UE performs measurement and carry out cell reselection of new candidate cell. This is based on certain criterion. Reselection process involves 2 steps
1.    Measurements Condition:  Specifies when to start measuring neighboring cells. Once condition is met UE measures the RSRP level of the E-UTRA cells on the current frequency and any inter-frequency and inter-RAT frequency carriers.

2.     Reselection Condition: Specifies reselection criteria for candidate cell. There are two different mechanisms for cell reselection:
 Legacy Based
Priority Based
Cell reselection can be either Legacy or Priority based.

Legacy Based
 This is classical Ranking based system and is applied to intra-frequency reselection.
• It is also applied to inter frequencies which are equally prioritized.
• UE applies cell ranking R criterion on serving cell and neighboring cell.

Priority Based
Priority values in the range [0..7] are used, where 0 indicates lowest priority and 7 indicates highest priority.
Priorities can be set for:
Inter Frequencies: Lower, Equal or Higher Priority
Inter-Rat Frequencies: Higher or Lower Priority

Equal priorities between different RATs are not supported


Idle Mode – Cell Reselection: Priority Based
CellReselectionPriority    :           Absolute reselection priority for E-UTRA or IRAT frequency

sNonIntraSearch :           Threshold for inter and IRAT frequency
threshXLow                    :           Threshold for Srx value of serving cell below which UE performs cell
 reselection towards a lower priority cell.

threshXLow                    :           Threshold for Srx value of target cell for cell reselection towards a
                                                lower priority Inter or IRAT frequency.
tReselectionEutra           :           Cell reselection timer value for EUTRAN


tReselectionUtra :           Cell reselection timer value for UTRAN 

LTE Idle Mode – Cell Reselection


After cell selection UE performs measurement and carry out cell reselection of new candidate cell. This is based on certain criterion. Reselection process involves 2 steps
1.    Measurements Condition:  Specifies when to start measuring neighboring cells. Once condition is met UE measures the RSRP level of the E-UTRA cells on the current frequency and any inter-frequency and inter-RAT frequency carriers.

2.     Reselection Condition: Specifies reselection criteria for candidate cell. There are two different mechanisms for cell reselection:
 Legacy Based
Priority Based
Cell reselection can be either Legacy or Priority based.

Legacy Based
 This is classical Ranking based system and is applied to intra-frequency reselection.
• It is also applied to inter frequencies which are equally prioritized.
• UE applies cell ranking R criterion on serving cell and neighboring cell.

Priority Based
Priority values in the range [0..7] are used, where 0 indicates lowest priority and 7 indicates highest priority.
Priorities can be set for:
Inter Frequencies: Lower, Equal or Higher Priority
Inter-Rat Frequencies: Higher or Lower Priority

Equal priorities between different RATs are not supported


Idle Mode – Cell Reselection: Priority Based
CellReselectionPriority    :           Absolute reselection priority for E-UTRA or IRAT frequency

sNonIntraSearch :           Threshold for inter and IRAT frequency
threshXLow                    :           Threshold for Srx value of serving cell below which UE performs cell
 reselection towards a lower priority cell.

threshXLow                    :           Threshold for Srx value of target cell for cell reselection towards a
                                                lower priority Inter or IRAT frequency.
tReselectionEutra           :           Cell reselection timer value for EUTRAN


tReselectionUtra :           Cell reselection timer value for UTRAN 

LTE Idle Mode Cell Selection


Once a cell meets all requirements, Criterion S is considered for cell selection.

Srxlev = [Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset) – Pcompensation] > 0

Where  

Pcompensation = [max (PEMAX – PUMAX , 0)]

Example: (Ignoring Offset and Pcompensation)

Srxlev = (Qrxlevmeas –Qrxlevmin) => -105 – (-120) = 15 db > 0


Parameter

Parameter
Description
QrxLevmeas
Measured RSRP value by UE (dBm)
Qrxlevmin
Required minimum RSRP level in the cell (dBm)
Qrxlevminoffset
Offset to Qrxlevmin
PUMAX
Maximum UE power according to its class
PEMAX
Maximum UE power to be used in a cell. Ericsson equivalent is pMaxServingCell


LTE parameters for IRAT cell reselection in WCDMA


arfcnValueUtranDl   : Indicates the ARFCN applicable for a downlink UTRA carrier frequency, 

cellReselectionPriority  : The absolute priority of the carrier frequency used by the cell reselection procedure. Default Value :7

ellReselectionPriority : The absolute priority of the concerned carrier frequency, as used by the cell reselection procedure. Default Value :6

pMaxUtra : The maximum allowed transmission power on the (uplink) carrier frequency. Default Value :33

sNonIntraSearch :Threshold for inter-frequency and inter-RAT measurements on frequencies of equal or lower priority. Default Value :0

threshServingLow Threshold for the signal strength of the serving cell, below which the UE performs cell reselection towards a lower priority inter-frequency or inter-RAT frequency. Default Value :0

threshXHigh : Specifies the threshold used by the UE when reselecting towards the higher priority frequency X than current serving frequency. Each frequency of UTRAN might have a specific threshold Default Value :4

threshXLow : Specifies the threshold used in reselection towards frequency X priority from a higher priority frequency. Each frequency of UTRAN might have a specific threshold. Default Value :0 

tReselectionUtra : Cell reselection timer value TreselectionRAT for UTRAN (1). Default Value :2

qQualMin : Minimum required quality level in the cell expressed in dB. Default Value :-119


qRxLevMin : Minimum required RX level in the cell expressed in dBm.

Bands for LTE


The latest revision of the LTE standard defines bands of operation, including both paired and unpaired spectrum. 1-32 bands are for paired (FDD) operation, while bands 33-40 are for unpaired (TDD) operation

Paired (FDD) and Unpaired (TDD) Operating Bands for LTE with Uplink & Downlink Frequency 



America Movil Signs Deal to Take Control of Telekom Austria


Maxico's America Movil is launching a takeover bid for the Telekom Austria Group with secure an agreement with the Austrian government's own holding company IAG.
America Movil and ÖIAG have initially signed a shareholders’ agreement to effectively pool their stakes in the telecoms company into a single syndicate.
America Movil already owns 26.4% of the company, while the government owns 28.4% of the telco.
Now that the agreement, which had been expected, has been signed, the two companies jointly control more than 30% of the shares and are required by Austrian stock market rules to launch a takeover bid for the company.
Subject to the closing of the takeover bid, the two shareholders will also pump an additional EUR1 billion into the company to help fund network upgrades.
America Movil will take over management of the company, although it is expected that the Austrian government would, through ÖIAG remain the larger of the two shareholders. ÖIAG also has the right to nominate the CEO and Chairman of the company.
Telekom Austria currently operates in Austria, Belarus, Bulgaria, Croatia, Serbia, Macedonia, Liechtenstein and Slovenia.
Post Date 24-April-2014



SS7


Definition:

Signaling System 7 (SS7) is an architecture for  performing out-of-band signaling in support of the call-establishment, billing, routing, and information-exchange functions of the public switched telephone network (PSTN). It identifies functions to be performed by a signaling system network and a protocol to enable their performance.

What is Signaling?
Signaling refers to the exchange of information between call components
required to provide and maintain service.

Long Code in CDMA


Long code in CDMA is a chip sequence which is 240 chips long, which repeats every 41.4 days. Its primary purpose is to assist in spreading the signal, to make spread spectrum work more efficiently. The Long code used on the reverse link is usually modified using the phone's ESN when in a call. See Long Code Mask.

WCDMA Basic

Download the WCDMA Basic document   Click here to Download 

Fading


FADING in Telecomunication
          The communication between the base station and mobile station in mobile systems is mostly non-LOS.
          The LOS path between the transmitter and the receiver is affected by terrain and obstructed by buildings and other objects.
          The mobile station is also moving in different directions at different speeds.
          The RF signal from the transmitter is scattered by reflection and diffraction and reaches the receiver through many non-LOS paths.
This non-LOS path causes long-term and short term fluctuations in the form of log-normal fading and rayleigh and rician fading, which degrades the performance of the RF channel

LONG TERM FADING
          Terrain configuration & man made environment causes long-term fading.
          Due to various shadowing and terrain effects the signal level measured on a circle around base station shows some random fluctuations around the mean value of received signal strength.
          The long-term fades in signal strength, r, caused by the terrain configuration and man made environments form a log-normal distribution, i.e the mean received signal strength, r, varies log-normally in dB if the signal strength is measured over a distance of at least 40l.
          Experimentally it has been determined that the standard deviation, s, of the mean received signal strength, r, lies between 8 to 12 dB  with the higher s generally found in large urban areas.

RAYLEIGH FADING
          This phenomenon is due to multipath propagation of the signal.
          The Rayleigh fading is applicable to obstructed propagation paths.
          All the signals are NLOS signals and there is no dominant direct path.
          Signals from all paths have comparable signal strengths.
          The instantaneous received power seen by a moving antenna becomes a random variable depending on the location of the antenna.







RICEAN FADING
          This phenomenon is due to multipath propagation of the signal.
          In this case there is a partially scattered field.
          One dominant signal.
          Others are weaker.






DOPPLERS SHIFT
          Dopplers shift is the shift in frequency due to the motion of mobile from the actual carrier frequency.
          Consider a mobile moving at a constant velocity v along a path segment having a length d between points X and Y while it receives signal from a remote source S.
          The Change in frequency due to dopplers shift is given by
                        fd = (v/l) * cos(f)
          It can be seen from the above equation that if the mobile is moving towards the direction of arrival of wave the dopplers shift is positive I.e. the apparent received frequency is increased. .


EGDE - Enhanced Data rates for GSM Evolution


(E)GPRS Network Infrastructure







How to calculate what
          No. of EGPRS resources used in 1 sector * No. of sectors : 2 x 3
           No. of time slot/sector * no of time slot used for EDAP :- 2 * 3 = 6
          So total time slots per site 6 + 6 = 12
          1 NSEI support 256 time slot with upgrade % as 10 so total no of time slots which can be equipped is 256 - 10% of 256 = 230.4 ~ 230
          So no. of sites per NSEI is 230/12 = 19.16 ~ 19
          So no NSEI required / BSC :  100 / 19 = 5.2 +1 (for future use) ~ 6
          2 NSEI supports 1 BCSU so no. of PCU required : 6/2 = 3
          No. of NSEI required is equivalent to the no. of Gb link = 3
          On 1 E1 we can get 31x64 = 1984 , so access rate can be given by 1 E1 = 1984/ access rate (256) = 1984 / 256  ~  7

Transmission requirement for EGPRS coding schemes in Abis interface






EDGE modulations

  
Scheme
Modulation
Maximum rate [kb/s]
MCS-9


8PSK
59.2
MCS-8
54.4
MCS-7
44.8
MCS-6
29.6 / 27.2
MCS-5
22.4
MCS-4


GMSK
17.6
MCS-3
14.8 / 13.6
MCS-2
11.2
MCS-1
8.8

 
 EDAP utilization
          6 EGPRS RTSLs (Dedicated + Default territory)
           50 % utilization assumed (3 Data Erlangs traffic)
           On average 3 RTSLs used





          RTSLs use MCS7 (44.8 kbit/s) with average C/I=13dB and throughput 30kbit/s
           Effective data rate factor excluding retransmissions over the air-interface is 30/44.8 ~ 0.7
           Slave group utilization is 0.7*0.5= 0.35