Data Transmission Flashcards
Mobile receives PDCCH
Every subframe, mobile reads control format indicator, establishes the size of DL control region , and locations of search spaces; process each PDCCH candidate
Mobile sends 3 types of uplink control info to BS
1) hybrid ARQ acks of BS DL transmissions
2) Uplink Scheduling Requests
3) Channel State information
CQI (channel quality Indicator
4 bit quantity which indicates the max data rate that the mobile can handle with a block error ratio of 10% or below
If BS does not reply to scheduling requests
After mobile reaches max number of sched requests w/o reply, triggers Rand Acc Proc
BS explicitly schedules all transmissions mobile carries out on?
physical uplink shared channel
If mobile wishes to transmit o PUSCH but does not have the resources to do so
it sends a scheduling request on physical uplink control channel; if doesn’t have resources for this, initiates random access procedure
1st step of Random Access
Mobile transmits a random access preamble on the physical access channel (PRACH)
Mobile receives what 3 things following rand access proc?
resources for an uplink transmission on the PUSCH, initial value ofr the uplink timing advance, C-RNTI
How does mobile read cell’s random access configuration?
From SIB 2
Persistant Scheduling Mode
UE can send data to network any time since network is sending UL Grant all the time
Steps of Non Persistent Scheduling
1) UE sends SR (Sched Req. on PUCCH)
2) Network sends UL Grant (DCI 0) on PDCCH
3) UE perform blind decoding - check PDCCH Search space and check if any info encoded with C_RNTI allocated
4) UE transmit PUSCH based on RBs specified by DCI 0
5) Network decodes it (knows the UL RB because it allocated it)
MIB carries what?
DL Bandwidth, number of transmit antenna, reference signal transmit power,
System Frame number (SFN), PHICH Configuration
HARQ
Works at Phy Layer but controlled by MAC layer
If received data has an error then the receiver buffers the data and requests a re-transmission from the sender; when receiver receives the retransmitted data, it combines it with buffered data prior to channel decoding and error detection
UL HARQ
HARQ is synchronous in the UL
PDCCH
physical channel that carries downlink control information (DCI)
PDCCH carries what
scheduling assignments (DCI 0 -uplink sched. assignment)
DCI stands for
Downlink control indicator
DCI answers what questions
Which resource block carries your data? What kind of demodulation scheme do you need to use to decode data?
DCI carries what information?
1) UL resource allocation (persistent and non-persistent)
2) Descriptions about DL data transmitted to the UE
BSR - Buffer Status Report
Provide NW with info about how much data in its buffer waiting to be transmitted
reference signal
UE uses to figure out DL power
Purpose of RACH
1) achieve up link synchronization between ue and eNB
2) obtain the resource for Message 3
Tracking Area Update
TAU
Registers the UE in the tracking area of the current cell
When is TAU invoked
UE mobility, periodic update, change in UE properties, MME load rebalancing, NAS signaling connection recovery
TAU if UE in ECM_CONNECTED state
already NAS signaling connection; UE sends Tracking area update req msg to eN using the ULInformation Transfer msg; eNB forwards to MME
If UE in ECM_IDLE state when TAU procedure inovked and MME changed
the new MME is updated with the UE context (UE ids, mobility state, security params) from the old MME
VNF (virtualized network functions)
one or more virtual machines with differing software functionality and process execution that replace custom hardware
Examples of network functions
modulations, coding, multiple access, ciphering
functional split
permits mapping of network functions to protocol layers and defining the placement of these layers w/in different NEs
Radio Bearer
transports control signaling or user data packets w/ common QoS between UE and eNB
2 types of radio bearer
signaling: Signaling Radio Bearer (SRB)
carry user data: associated w/ EPS bearer
default radio bearer
able to carry various types of traffic w/o QoS; typically created during attach proc
dedicated radio bearer
carries specific data flow identified by Traffic Flow Template (TFT) with a given QoS; est. during Attach or after
Ciphering applies to what msgs
NAS signaling, RRC signaling on SRB1 and SRB2, user plane data
Integrity Protection Aplies to:
NAS signaling msgs, control plane data, RRC signaling on SRB1 and SRB2
Ciphering and integrity applied after what?
activation of security for both NAS and AS, only when UE in RRC_CONNECTED, when SRB1 is establish (SRB0 has no ciphering or integrity)
EPS security context
state between UE and core network (CN)
EPS NAS security context
exists in RRC_IDLE and RRC_CONNECTED; stays valid when RRC connection related; use Kasme
EPS AS security context
only in RRC_CONNECTED state; when RRC connection established, a new EPS AS security context is set up
AKA
LTE-EPS authentication and key agreement
EPS AKA
provides mutual auth between UE and NW, establishes Kasme, takes place during attach proc and Tracking Area UPdate (TAU) proc
Who initiates AKA proc?
Network always initiates, UE can reject
Power on Sequence (mobile switches on)
1) mobile selects a public land mobile network (PLMN) that it will register with
2) mobile (optionally) ask user to select a closed subscriber group (CSG)
3) mobile selects cell that belongs to selected network and CSG
In network selection proc, mobile selects what to register with?
public land mobile network (PLMN)
If mobile can’t find registered PLMN in network/cell selection, it does hat?
scans all LTE carrier frequencies it supports and identifies networks it can find; find strongest LTE cell on each freq, read SIB and identifies network
automatic network selection mode
mobile runs in priority order through a list of networks that it should treat as home PLMNs, runs cell selection proc when find network
manual mode
mobile presents user with the list of networks that it has found, user then selects preferred network
2 Parameters for RRC Connection Request
1) Non-access stratum (NAS) identity (S-TMSI) or random
2) establishment cause
How does mobile send RRC Connection Request
Radio Bearer 0 (configuration for this sent by BS in SIB2); message sent on common control channgel, uplink shared channel, and physical uplink shared channel
eNB response to RRC Connection Request
RRC Connection Setup
What is in the RRC Connection Setup
configures mobile’s physical layer and mac protocols; PUCCH resources, time for buffer status reporsts, hybrid ARQ transmissions
RRC Connection Setup Complete
mobile sends to eNB after receiving the RRC Connection Setup msg
What’s in the RRC Connection Setup Complete msg?
1) Mobile identifies PLMN it would like to register with
2) Globally unique identity of MME previously serving mobile (extracted from GUTI)
3) EPS mobility management message that BS will forward to MME
Objectives of Attach Proc
1) mobile registers location with a serving MME
2) NW configures signalling radio bearer 2, which carries NAS signalling
3) Network gives mobile an IP
4) NW sets up default EPS bearer
IMEI
International Mobile Equipment Identity
Update location request
new MME sends the mobile’s IMSI to the HSS
User specific key K
1:1 mapping with IMSI
User specific key k derives CK and Ik, which are used to derive what?
Kasme (access security management entity) key
From Kasme, derive 3 further keys?
Knasenc, knasint, Kenb
RRC_CONNECTED state
mobile is assigned to a serving eNB, and can freely communicate w/it using signalling msgs on SRB 1
RRC_IDLE
radio access network knows nothing about the mobile, so no serving eNB is assigned and SRB 1 is torn down; RAN can still page mobile
EMM Service Request
Mobile asks the serving MME to move it to ECM-CONNECTED
SIM card
runs USIM, stores user info (phone number, home network id), carry out security calculations using secure keys
mobile range of capabilities
max data, RATs supported, carrier frequencies they can transmit and receive
S1 interface
base station connected to EPC
S2 interface
base station to base station, used for signalling and packet forwarding during handover
MME pool area
mobile can move without changing a serving MME
M-TMSI
identifies a mobile to its serving MME
MME communicates to mobile
through AS and NAS; the high-level signalling messages lie in the non-access stratum and are transported using the access stratum protocols
MAC protocol
carries out low-level control of the physical layer, particularly by scheduling data transmissions between the mobile and base station
radio link control (RLC) protocol
maintains the data link between the two devices
What does PDCP stand for?
packet data convergence protocol
What does PDCP do?
carries out higher-level transport functions that are related to header compression and security
RRC protocol
base station controls a mobile’s radio communications by signalling
MME controls’ a mobile’s high-level brehaviour using two protocols that lie in the air interface’s NAS
EPS session management
EPS mobility management
EPS session management protocol
controls the data streams through which a mobile communicates with the outside world
EPS mobility management protocol
handles internal bookkeeping w/in the EPC
How does network transport EMM and ESM messages
embeds them into lower level RRC and S1-AP messages and then by using the transport mechanisms of the Uu and S1 interfaces
Diameter protocol
HSS and MME
UE capacity enquiry and response
serving eNB wishes to find out the mobile’s radio access capabilities
What are RRC messages known as?
UL Information Transfer/DL Info Transfer
What are S1-AP messages known as?
Uplink NAS transport and downlink NAS transport
signalling radio bearers
carry signalling messages between the mobile and base station
SRB 0
mobile and bs use to establish communications in RRC connection establishment; config defined in RRC messages known as system info messages which are broadcasted from eNB
SRB 1
configured using messages exchanged on SRB0, transports some EMM and ESM message
SRB 2
configured using signalling messages that are exchanged on SRB!, when mobile establishes communications with EPC - used to transport all of the remaining EMM and ESM messages
3 parts of physical layer
transport channel processor - error management
physical channel processor - OFDMA, SC-FDMA, and multiple antenna transmission
analogue processor - radio frequ
logical channel
data and signalling messages carried on these between RLC and MAC
transport channel
between MAC and physical layer
physical data channel
differnet levels of the physical layer
where is control info created
in the transmitter by the transport channel processor
Dedicated control channel
carries the mobile specific signalling messages on rignalling radio bearers 1 and 2 for mobiles in the RRC_CONNECTED state
BCCH - broadcast control channel
carries RRC system info message; base station broadcasts to tell mobiles about cell configuration (SIBs and MIB)
What does PCCH stand for?
paging control channel
common control channel
carries messages on signalling radio beaer 0, for mobiles that are moving from RRC_IDLE to RCC_CONNECTED
DRS
demodulation reference signal - mobile sends on uplink at same time as PUSCH and PUCCH as a phase reference for channel estimation
SRS
mobile sends sounding reference signal for power reference at times configured by base station
