Initial Acquisition Procedure

-Qualcomm University

LTE RRC Connection Reject Message

According to the 3GPP TS 36.331 , RRC CONNECTION REJECT message is used to reject the RRC connection establishment. This message includes the IE waitTime which can be in the range from 0 to 16 seconds. Optionally, the NW can include the IE extendedWaitTime for the purpose of Delay Tolerant access requests

          Upon receiving the RRC CONNECTION REJECT message, the UE should start timer T302, with the timer value set to waitTime. The UE is not allowed to send another RRCConnectionRequest for mobile originating calls, mobile originating signalling, mobile terminating access and mobile originating CS fallback on the same cell on which RRC CONNECTION REJECT is received until the expiry of T302

 The following differences are noted as compared to UMTS RRC CONNECTION REJECT:

1.             There is no RejectionCause in the case of LTE

2.             RedirectionInfo which is used to redirect the UE to another frequency/RAT is not present in the case of LTE

3.             LTE requires the higher layers to initiate new RRC CONNECTION REJECT after receiving RRC CONNECTION REJECT, where as in the case of UMTS, the procedure is repeated for N300 times

BLER and SIR

Block Error Rate (BLER) is an analysis of transmission errors on the radio interface.

It is based on analysis of cyclic redundancy check (CRC) results for radio link control (RLC) transport blocks and computed as below:

Signal-to-Interference Ratio (SIR), also known as the carrier-to-interference ratio (C/I, CIR), is the quotient between the average received modulated carrier power and the average received co-channel interference power.

For UL Power Control:

Example: Mobility movement > Handover trigger > SIR Error > UL BLER

Spreading Factor (SF) or Processing Gain

Spreading factor (SF) is the ratio of chip rate to bit rate OR the ratio of the chips to baseband information rate. As after spreading, A single bit of the user data is called chip.

Spreading factor is the concept of CDMA used in UMTS. Spreading factors vary from 4 to 512 in FDD UMTS.

Spreading factor in dB indicates the processing gain as in a spread spectrum system, the processing gain is the ratio of the spread (or RF) bandwidth to the unspread (or baseband) bandwidth. It is the ratio of the signal-to-noise ratio (SNR) of a processed signal to the SNR of the unprocessed signal. The lower the spreading factor, the higher the data rate.

Timing Advance (TA) in LTE

Posted on 01. Sep, 2010 by agaur in Blog, Timing Advance, LTE

Source: lteworld.org

In GSM system MS sends its data three time slots after it received the data from the BTS.  This is ok as long as MS-BTS distance is small but increasing distance requires consideration of propagation delay as well. To handle it Timing advance (TA) is conveyed by network to MS and current value is sent to the MS within the layer 1 header of each SACCH. BTS calculates the first TA when it receives RACH and reports it to the BSC and BSC/BTS passes it to UE during Immediate Assignment. 

In UMTS Timing Advance parameter was not used but in LTE Timing Advance is back. 

In LTE, when UE wish to establish RRC connection with eNB, it transmits a Random Access Preamble, eNB estimates the transmission timing of the terminal based on this. Now eNB transmits a Random Access Response which consists of timing advance command, based on that UE adjusts the terminal transmit timing.

The timing advance is initiated from E-UTRAN with MAC message that implies and adjustment of the timing advance.

3GPP TA Requirements

• Timing Advance adjustment delay 

UE shall adjust the timing of its uplink transmission timing at sub-frame n+6 for a timing advancement command received in sub-frame n.

• Timing Advance adjustment accuracy 

The UE shall adjust the timing of its transmissions with a relative accuracy better than or equal to ±4* TS seconds to the signalled timing advance value compared to the timing of preceding uplink transmission. The timing advance command is expressed in multiples of 16* TS and is relative to the current uplink timing.

Maintenance of Uplink Time Alignment

The UE has a configurable timer timeAlignmentTimer which is used to control how long the UE is considered uplink time aligned

• when a Timing Advance Command MAC control element is received  then UE applies the Timing Advance Command and start or restart timeAlignmentTimer.
• when a Timing Advance Command is received in a Random Access Response message then one of following action is performed by UE

- if the Random Access Preamble was not selected by UE MAC then UE applies the Timing Advance Command and starts or restarts timeAlignmentTimer.

- else if the timeAlignmentTimer is not running then UE applies the Timing Advance Command starts timeAlignmentTimer; when the contention resolution is considered not successful  then UE stops timeAlignmentTimer.

- else ignore the received Timing Advance Command.

• when timeAlignmentTimer expires UE flushes all HARQ buffers, notifies RRC to release PUCCH/SRS and clears any configured downlink assignments and uplink grants.

Timing Advance Command MAC Control Element

The Timing Advance Command MAC control element is identified by MAC PDU subheader with LCID value =  11101 (Timing Advance Command) .

It has a fixed size and it consists of a single octet as show below.

Timing Advance Command MAC control element has following fields.

• R: reserved bit, set to "0"
• Timing Advance Command: This field indicates the index value TA (0, 1, 2… 63) used to control the amount of timing adjustment that UE has to. The length of the field is 6 bits.

Source: 3GPP specifications (36.133 & 36.321)

G-NetTrack

G-NetTrack is a fieldtest/netmonitor Android application for LTE/UMTS/GSM/CDMA/EVDO network. 
It is very awesome!!

Below is the link, Enjoy :D
https://play.google.com/store/apps/details?id=com.gyokovsolutions.gnettrack