Key Features of LTE

·         Multiple access scheme : Downlink: OFDMA  & Uplink: Single Carrier FDMA (SC-FDMA)

·         Adaptive modulation and coding

·         DL modulations: QPSK, 16QAM, and 64QAM

·         UL modulations: QPSK and 16QAM

·         Rel-6 Turbo code: Coding rate of 1/3, two 8-state constituent encoders, and a contention-free internal interleaver.

·         Bandwidth scalability for efficient operation in differently sized allocated spectrum bands

·         Possible support for operating as single frequency network (SFN) to support MBMS

·         Multiple Antenna (MIMO) technology for enhanced data rate and performance.

·         ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer.

·         Power control and link adaptation

·         Implicit support for interference coordination

·         Support for both FDD and TDD

·         Channel dependent scheduling & link adaptation for enhanced performance.

·         Reduced radio-access-network nodes to reduce cost,protocol-related processing time & call set-up time

Paging Success Rate in 2G

The paging success rate measures the percentage of how many

paging attempts that have been answered, either as a result of the

first or the second repeated page.

PSR = Time of Paging Responses / Time of Paging

Possible reasons for poor Paging Performance could be:

 Paging congestion in MSC

 Paging congestion in BSC

 Paging congestion in Base Transceiver Station (BTS)

 Poor paging strategy

 Poor parameter setting

 Poor coverage

 High interference

LTE Throughput Calculation

Solution:

1 RB = 12 sub-carriers

1 Sub-carrier = 7 OFDM symbols in time domain = 7 Resource elements

Thus total OFDM symbols in 1 RB = 12 X 7

With 64 QAM 1 symbol = 6 bits

Thus total bits in 1 RB = 12 X 7 X 6 transmitted in 0.5 msec

With 20 MHZ BW, 100 RB are transmitted

Thus total bits in 100 RB = 12 X 7 X 6 X 100 transmitted in 0.5 msec

Thus in 1 msec, total bits transmitted = 12 X 7 X 6 X 2 X100

In 1 sec, total transmitted bits = 12 X 7 X 6 X 2 X 100 X 1000 = 100.8 Mbps

This is possible with Single antenna configuration

But with 4 x 4 MIMO

Maximum throughout = 4 X 100.8 = 403.2 Mbps

LTE – Resource Block

›       Resource Block

–        1 Slot (0.5ms) and 12 sub-carriers.

–        1 User is Scheduled every TTI (1ms), which means a minimum of 2 consecutive resource blocks in time at every scheduling instance.

2G Timer parameter

T3105 :Time between repetition of physical information to MS. Will be repeated NY1 times.

T3101 : Guard time for Immediate Assign. Started as 'IMM_ASS_CMD' is sent to BTS and stopped by reception of 'EST_IND' from BTS.The allocated channel will be released at timer expiry.

T3260 : The timer is started when AUTHENTICATION REQUEST is sent from MSC. The timer is stopped when AUTHENTICATION RESPONSE is received in MSC. The connection is released with a CLEAR COMMAND at timer expiry.

T3212 : Time between periodic update of MS. SET by the MML command RLSBC. The value is sent to the MS in system information. The MS will do periodic update, if it is residing in the same location area at a time interval exceeding T3212 . If the MS is roaming to a new location area, update will be done anyway and the time to next periodic update will start counting from zero again.

RLINKT (T100)  : Time before an MS disconnects a call due to failure in decoding Slow Associated Control Channel (SACCH) messages. The parameter is given as number of SACCH periods (480ms).

T3101 : Guard time for Immediate Assign. Started as 'IMM_ASS_CMD' is sent to BTS and stopped by reception of 'EST_IND' from BTS.The allocated channel will be released at timer expiry.

T3105 : Time between repetition of physical information to MS. Will be repeated NY1 times.

T3109  : Guard timer for channel release indication when clearing mobile station. Started by sending DEACT_SACCH to BTS and stopped by reception of 'REL_IND' from BTS. It is controlled by RLINKT.

T3111 : Delay for connection release. Started as REL_IND is received from BTS. When expired RF_CHAN_REL is sent to BTS.

RLINKUP : Time before a BSC disconnects a call due to failure in decoding UPLINK Slow Associated Control Channel (SACCH) messages. The parameter is given as number of SACCH periods (480ms).

T3126 : This timer is started either after sending the maximum allowed number of CHANNEL REQUEST messages during an immediate assignment procedure or on receipt of an IMMEDIATE ASSIGNMENT REJECT message, whichever occurs first. It is stopped at receipt of an IMMEDIATE ASSIGNMENT message, or an IMMEDIATE ASSIGNMENT EXTENDED message. At its expiry, the immediate assignment procedure is aborted.

T203 : Timer that supervises the maximum time without frames being exchanged on a A-bis link (LAPD).

RACH in 2G

Random Access (RACH) Success :
Random Access Channel (RACH) is used by the MS on the “uplink” to request for allocation of an SDCCH. This request from the MS on the uplink could either be as a page response (or incoming call) or due to user trying to access the network to establish a call. Availability of SDCCH at the RBS will not have any impact on the Random Access Success.

The number of times an MS tries to access the network (repeated access in the event of no response from the BS in the form of immediate assignment or immediate assignment reject on AGCH) is decided by the BSS parameter MAXRET (maximum number of retransmissions) and the randomness in the time interval between each of these access request is defined by the parameter TX.

Random Access Success Rate = (CNROCNT)/ (CNROCNT+RAACCFA) * 100

RAACCFA: Failed Random Access
CNROCNT: All accepted Random Access

Root cause analysis of poor Random Access Success
  Fish Bone diagram for root cause analysis of poor Random-Access Success Rate

Reason for Poor RACH Failure.

Poor BSIC Plan
Poor BCCH plan
Poor Coverage / Spillage
Phantom RACH
ACCMINand CRO
Faulty Antenna / Cable.
MAXRET and TX
 

GSM

What is GSM?

GSM (Global System for Mobile communications) is an open, digital cellular technology used for transmitting mobile voice and data services.

What does GSM offer?

GSM supports voice calls and data transfer speeds of up to 9.6 kbps, together with the transmission of SMS (Short Message Service).

GSM operates in the 900MHz and 1800MHz bands in Europe and the 1900MHz and 850MHz bands in the US. GSM services are also transmitted via 850MHz spectrum in Australia, Canada and many Latin American countries. The use of harmonised spectrum across most of the globe, combined with GSM’s international roaming capability, allows travellers to access the same mobile services at home and abroad. GSM enables individuals to be reached via the same mobile number in up to 219 countries.

Terrestrial GSM networks now cover more than 90% of the world’s population. GSM satellite roaming has also extended service access to areas where terrestrial coverage is not available.

In India GSM operates in 900MHz and 1800MHz Band and 1900MHz band are reserve for Military purpose.

900MHz Bandwidth is 25MHz, Channel Bandwidth is 200KHz, & ARFCN is 125
1800MHz Bandwidth is 75MHz,  Channel Bandwidth is 200KHz, & ARFCN is 374.