Fast Dormancy (FD)

Fast Dormancy (FD) is a wireless technology feature introduced to improve battery life on the mobile devices.

Fast dormancy is a way by which UE  informs the network to release the RRC connection. (Termination of RRC connection is always triggered by network)

UE consumes more battery when in connected state, so when there is no data to transfer UE informs to network to release its RRC connection to save the battery power.

However with bursty data traffic nature UE's may end up sending moreRRC connection request and  SCRI(signalling connection release indications) to network.

From Rel-8 3GPP inroduced a timer T323 whose value is brodcasted in SIB1.

If network supports this rel-8 fast dormancy feature UE should not trigger fast dormancy request until the T323 timer expiry.

Device to Device Communication

• Device to Device Communication has been the latest reasearch topic for LTE advanced. Which enables UE's those are in the proximity to discover and communicate with each other.
• Various use cases involved are
• Social gaming
• Commercial advertisements
• Pubic safety purposes
• Network offloading  

• Enormous operator benefits involved using device to device communications such as
• Peak data rates: as the UE's are near by due to which good radio conditions can enables higher modulation schemes.
• Low latency: No need to go through all the network entities involved in data communication.
• Capacity: Due to spectrum re use UE can accommodate more users
• Extended Coverage : UE's in network coverage can provide services to UE's which are present out side of network coverage (Relay operation)
• With the advancement in the technology and social life opened new ways to communication.
• Prose is a feature that enables operator network controlled discovery and communications between UEs that are in proximity.
• It allows UE's in proximity will discover other UE's in their vicinity and start communication directly with less involvement of network.
• Various use cases involved such as location based advertising (Ads by shops to customers passing near by), social networking applications (facebook, twitter),network off loading and Public safety etc.
• The communication path could for example be established directly between the UEs or routed via local eNB(s).

Discovery Types : 

• Open ProSe Discovery: is ProSe Discovery without explicit permission from the UE being discovered.
• Restricted ProSe Discovery: is ProSe Discovery that only takes place with explicit permission from the UE being discovered. UE's can have a feature enabled whether it can be discovered by other UE's are not (privacy).
• Operator can change dynamically the range of the proximity per user/application. 

Disovery Models :

Model A:

• Model A is push model like "i am here". used for both open and restricted discovery.

Model B:

• Model B is pull model like "who are there" or "Are you there". it is used for restricted discovery. 

3GPP TR 22.803,3GPP TS 23.303

T3412 - Periodic Tracking Area Update timer

Periodic Tracking Area Update procedure to used to periodically notify the availability of the UE to network.

UE needs to notify its presence to the Network periodically and is controlled using T3412 timer in LTE.

One of the reasons for this is that at any time network will be aware of the UE's presence at a granularity of Tracking Area. Which will be needed for cases such as paging.

Default value of this timer is 54 min.

The value of this timer is provided by the network operator during the attach and tracking area updating procedures

If this value is not present or value is zero (0) UE should not trigger periodic tracking area procedure.

T3412 contains two parameters

i)timer_unit

   If timer unit is 2 it represents that timer value is represented in deci hours.

ii)timer value

    If timer value is 1 it means 6 mins (if timer unit is 2)

T3412 will be stopped when UE enters EMM-CONNECTED or EMM-DEREGISTERED mode.

T3412 will be reset and started with initial value when UE moves from EMM-CONNECTED to EMM-IDLE mode.

When the network includes T3412 extended value IE in the ATTACH ACCEPT message or TRACKING AREA UPDATE ACCEPT message, the network uses timer T3412 extended value IE as the value of timer T3412

On expiry of the timer UE initiates Periodic TAU Request if the UE is not registered for the emergency bearer services or T3423 running.Implicit detach from network if the UE is attached for emergency bearer services.

Network will maintain a mobile reachable timer which is 4minutes greater than T3412. If UE not updated TAU with in mobile reachable timer network shall implicitly detach the UE

According to 3GPP 24.301