1. Introduction to IOT
2. Requirements, Challenges and solutions
What is IoT?
IoT is a network of devices embedded with sensors and
network connectivity that enables them to collect and
How it works?
Collection of data
Transmission of selected data through a communication
Assessment of the data
Response to the available information
Example: Smart Parking
Collection of data -
System relies on sensors embedded in the parking area.
Transmission of selected data through a communication
When a car parks on the sensor, it is detected and the sensor
relays the information wirelessly to the gateway. Gateway
sends the information through network to the database.
Assessment of the data –
Information is updated in the database and a central control can
perform analytics about the parking area occupancies
according to time and day.
Response to the available information –
Occupancy is reported to users via apps and panels in the street.
3GPP has been working on 3 different IoT standard
•LTE-M based on LTE evolutions, Cat0(rel 12) and cat-
•EC-GSM – A narrowband solution based on GSM
•NB-LTE- A narrowband cellular IoT solution, also
known as clean state solutions, Cat200KHz.
Later, EC-GSM and NB-LTE, were combined for
standardization as a single NB-IoT technology.
NB-IoT would support three modes of operation :-
1. ‘Stand-alone operation’ utilizing, for example,
the spectrum currently being used by GERAN
systems. i.e. replacing a GSM carrier with NB-IoT
2. ‘Guard band operation’ utilizing the unused
resource blocks within a LTE carrier’s guard-band,
3. ‘In-band operation’ utilizing resource blocks
within a normal LTE carrier.
Requirements & Challenges
Cheap devices => Provisioning of low cost & low
Battery Life > 10 yrs => UE Power Consumption
MTC devices installed in basements or covered by
insulation leading to penetration losses => Coverage
Improvement of 20dB is targeted as compared to legacy
LTE(category 1 UE- 142.7 dB).
Millions of connected devices expected => Congestion
Low data rate requirements => choosing appropriate
Battery Life solution:
UE Power Consumption
4 solutions have been proposed by 3GPP to
lower UE’s power consumption-
1. Extended DRX cycle in IDLE mode.
2. Extended DRX cycle in CONNECTED
3. Power Saving Mode.
4. Reducing the RF Bandwidth
Basics of Discontinous
Mechanism to save UE energy
UE keeps it’s receiver circuitry off
for certain time period i.e. it goes
into sleep and wake up states.
In wake up state it listens to PDCCH
whereas in sleep state it’s receiver
ON Period – Period during which UE should monitor PDCCH.
OFF Period – UE enters sleep state.
DRX Cycle – 1ON + 1 OFF Period.
DRX Inactivity Timer- After reception of PDCCH in ON period, UE
starts this timer and monitors PDCCH in every consecutive
subframe till it expires.
DRX Retransmission Timer- When data on PDSCH for a HARQ
process is nacked by UE, it knows that it will be retransmitted by
eNB, so it starts this timer during which it’ll not go into sleep mode
and listen to PDCCH continously for the retransmission.
DRXStartOffset - Subframe when DRX cycle starts.
DRX short cycle is optional and is for applications like VOIP that
require transmission of small amount of data at short, regular
DRX can be implemented in IDLE as well as Connected
In Idle mode, DRX is same as paging cycle
In Connected mode, UE needs to listen to PDCCH for data
UE is in RRC Connected mode and is continuously monitoring
PDCCH. At this point, there is DL Grant and downlink data. The DRX
inactivity timer and the main RRC Inactivity timer are restarted
There is UL grant for UE. With DL Grant both DRX and RRC
inactivity timers are restarted. 4 ms later UE sends data in uplink
The DRX Inactivity timer is expired since there were no further
grants in uplink or downlink. Though UE was constantly monitoring
PDCCH. UE now enters the short DRX cycle. The battery savings
have just started
The DRX short cycle timer got expired therefore UE will end up its
short DRX cycle and enter the long DRX cycle
The main RRC inactivity timer got expired since there was no
activity in uplink or downlink for the duration for RRC Inactivity
timer. The UE will go to RRC IDLE state. In idle state UE will use
paging DRX cycle
How is it configured?
DRX in IDLE mode can be cell
specific or UE specific.
Default DRX cycle or cell specific DRX cycle is configured
at eNB and broadcasted in SIB2 to ue’s
Dedicated or UE specific DRX value is indicated by UE to
MME in attach request .
Both eNB and UE uses smaller of the 2 values.
Only On-duration and inactivity timer are signalled to UE
Extended DRX cycle in IDLE
On increasing DRX cycle length in idle mode i.e. paging
cycle length, UE can go to sleep for longer duration but
can remain attached.
Issues and impact
Now, both eNB and UE adopt UE specific extended DRX
value. This can impact SIB reading-
Suppose extended DRX cycle length is longer than
modification period. In this case, eNB would change SI
and start broadcasting SIB’s but UE would not listen. In
legacy LTE, BCCH modification period is a multiple of
default DRX value. Hence, UE could read modified sib’s.
Perform cell search and SI reading before the
R2-132394 proposes a power consumption model with following parameters-
P one normal DRX cycle = Tsleep * Psleep + (Tprepare + Ton-duty)
Tsleep = DRX cycle – Tprepare – Ton-duty
e.g. when DRX cycle is 2.56sec,
P one normal DRX cycle = (2560 – 34 – 1) * 0.01 + (34 + 1) * 1 =
In case of extended DRX (> BCCH modification period):
Pone extended drx cycle = Tsleep * Psleep + (Tprepare + Ton-duty
+ TSI-reading + Tcell-detection) * Prx
Tsleep = Extended DRX cycle – Tprepare – Ton-duty – TSI-reading
Tprepare = 0 ; coz it would be taken care of in Tcell-detection.
e.g. when extended DRX cycle is 10.24sec (= one System Frame),
P one extended drx cycle = (10240–1–200–600) * 0.01 +
(1+200+600) * 1 = 895.39
For the power consumption comparison between
the normal DRX case and the extended DRX case,
above P one normal drx cycle should be
multiplied by (Extended DRX cycle ÷Normal DRX
Ex, when the extended DRX is 10.24sec and the
normal DRX is 2.56sec, the power consumption
for the normal DRX shall be multiplied by 4.
Gain by the Extended DRX can be seen when the
Extended DRX is longer than 6 system frame
length and from there the more the DRX is
extended the more gain can be observed.
Extended DRX cycle in
It refers to increasing the DRX cycle length in connected
mode, similar to idle mode extension.
Issues and impacts
The device should be delay tolerant since, extending
the cycle length would mean delay in dl data.
If there is no activity in ul and dl, RRC inactivity timer
expires and UE goes into idle mode and RRC connection
is released. We need to increment it’s value.
When long DRX cycle is used, re transmissions on higher
layers needs to be minimized. Without adjusting the
retransmission timers, longer DRX upto several minutes
may impact the reachability of the UE. For ex, when
TCP sender sends data to an MTC device, it starts a
retransmission timer and if it doesn't receive ack till it's
expiry it'll retransmit and in worst case it would be
unable to transmit it.
Power Saving Mode(PSM)
After a UE goes into idle mode, it releases RRC connection.
It then starts an active timer while performing all idle
mode functions i.e. PLMN selection, cell
selection/reselection, paging. When active timer expires,
UE enters into PSM and starts a Periodic Update
Timer, expiry of which will indicate the end of PSM. In this
time, the UE stops reading paging or performing any
AS(cell/PLMN selection) or NAS(MM procedures) functions.
Also, network should not send any data or page the device.
When UE wants to use PSM, it'll request an active timer in
attach/TAU request. If eNB supports PSM it'll select a timer
value from the UE given value or MME given configuration.
Afterwards, if UE wants to change it's value due to certain
condition changes, it'll request the value in TAU procedure
Max duration of PSM is 12.1 days.
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Issues and Impacts
•A transition within IDLE state is required.
•Most networks today expect contact with device every 2-4
hours, otherwise it is considered as not reachable and it
quietly detaches it from the network so that it limits the
devices it needs to keep track of. But now, n/w needs to
maintain a very large number of devices that will contact
the n/w in a week or two.
An optimization at eNB would be to decide a PO within the
active time period. When eNB receives a paging message
from MME, it finds a PO within active time period, if it is
unable to find such PO it'll stop paging at RAN.
E-DRX vs PSM
Extended DRX cycle Power Saving State for devices
Applicability - UEs that can always tolerate
traffic with longer access delays
for MT services,
- Relatively infrequent data.
Same as for ‘extended DRX cycle’
Power saving gain s Reduction of :
- paging monitoring
Reduction of :
- paging monitoring
- SIB monitoring
- cell/RAT/PLMN selection
- MM procedures
Impact on mobility - Supports mobility
- Cell reselection may suffer
latency due to possibly reduced
frequency of measurements
- No mobility support when UE is
in power saving state (UE
executes cell selection when
leaves the power saving state)
Impacts to specification - Potential modification to paging
if DRX Cycle is extended
beyond 1024 radio frames in
LTE or 4096 radio frames in
- Updates to RRM requirements
may be necessary (RAN4
performance requirements may
need to be updated for longer
- UE and eNB capability support
- No new RRC state is needed,
transitions within the RRC idle
state need to be defined
(including a new timer and
corresponding NAS signalling).
- Negotiation/confirmation of
UE/network capability of this
Some MTC UE’s are installed in basement or covered by
insulation, leading to penetration losses
Coverage improvement of 20dB is required compared to
category 1 UE.
Basic Terminology – What is
Coupling Loss –
Total channel loss over the link b/w UE antenna ports and eNB antenna ports,
Includes path loss.
Limit value of coupling loss at which service can be delivered and defines the
coverage of the service.
It is a range of power within which receiver can listen.
Sender's TX power - Loss = Receiver's Sensitivity.
=> UL MCL = UL max TX Power - eNB Sensitivity
And DL MCL = DL max TX Power - UE Sensitivity
3 Solutions have been proposed
by 3gPP to enhance coverage
1. TTI Bundling Enhancement
3. PSD Power Boosting
Repetitions means to transmit a TB in more than 1 sf's.
2 Coverage Enhancement (CE) modes are defined-
Mode 1 describes behaviors agreed for no repetitions or
small number of repetitions.
Mode2 describes behaviors agreed for large number of
A CE level is configured for all channels in a UE.
One CE level can be configured with a set of repetition
numbers at least for PDSCH, PUSCH & MPDCCH
Impact & Issues
Allowing repetition for channels can have an impact on
how the channels are allocated.
For ex, PUCCH resource determination from ECCE
linkage assumes fixed timing gap b/w PUCCH and
PDSCH, but due to different number of repetitions, it
could vary, leading to resource collision.
Basics of TTI Bundling
If we talk about a normal uplink TB, it is converted into
various redundancy versions and first redundancy
version is sent in a subframe followed by consecutive
transmissions based on HARQ result.
TTI Bundling is a mechanism in which UE transmit
a PUSCH (with different redundancy versions) all in
multiple subframes continously. i.e. UE sends the same
packet but with different error correction and detection
bits in consecutive sf's w/o waiting for HARQ result. The
retransmission of TTI bundle is also a TTI bundle.
Why TTI Bundling
To increase the decoding possibilty of TB for cell edge
UE's where the coverage is poor. Coz if we know
coverage is poor, then instead of waiting for HARQ
nack's, we can transmit all RV's together, decoding
which would be better.
On increasing redundancy, SINR would decrease leading
to greater MCL.
It saves a lot of signalling overhead as only 1 PDCCH
assignment is needed for multiple transmissions. Also, it
sends ACK/NACK for the entire bundle rather than every
1 RLC header is used for all versions and 1 HARQ process
1. Current supported TTI Bundle size- 4
2. Max allowed PRB per sf - 3
Scope of further enhancement for MTC UE's-
1. Introduction of a new TTI Bundle size,
2. Introduction of a new RTT and HARQ timing for
a bundle size
3. Allow more than 3 PRB allocated per subframe.
Introduction of a new
TTI Bundle size-
If we increase the bundle size, decoding possibility
increases but at the expanse of more PRB resource usage
and slightly longer delay.
It has been experimented that on increasing bundle size
from 4 to 8 approx 3DB gain can be expected.
What should be max Bundle
Inter arrival time of VOIP packets is 20msec
i.e. AMR codec provides packets at 20 msec
interval. Hence, it was a natural choice to
limit the max number of TTI for packet to be
20. However, since majority of packets use
less than max TTI with 2% bler target, it will
not result in queue build up.
For ex, 8 TTI bundling with max 3 HARQ
transmissions(upto 24 TTI's per VOIP packet)
provided a 1DB gain over 4 TTI Bundle with 4
3GPP has not concluded a figure for this yet.
Introduction of a new RTT and
HARQ timing for a bundle size-
Reduced round trip time can bring
benefits for more energy
accumulation for VoIP within given
delay budget. However, it will
become difficult for scheduler to
effectively cohandle rel 8/9/10 UE's
Allow more than 3 PRB
allocated per subframe-
This allows flexibility in UE scheduling. Limiting it to 3
PRB's may not allow UE to take full advantage of
dynamic change in channel and limit it's performance.
It is possible that the packet is decoded in the first
transmission, then it leads to wastage of time and more
energy consumption than needed.
Provisioning of Low Cost &
We’ll discuss 3 solutions for reducing the cost and
complexity of a device-
1. Reduction Of Maximum Bandwidth.
2. Reduction of supported downlink transmission modes.
3. Reduction of transmit power.
Reduction Of Maximum
It has been experimented by various companies and
concluded that upto 40-50% cost savings can be
achieved by reducing bandwidth.
Reducing the max bandwidth from 20MHz to 1.4 MHz has
There are 3 cases-
Reduce bandwidth for both RF and Baseband
Reduce bandwidth for baseband only
Reduce bandwidth for baseband for data channel only
Impacts and Issues
For all the options, coverage of PDSCH and PUSCH can
be affected because of loss in frequency selective
Power consumption is minimized as discussed earlier.
However, due to degradation in PDSCH and PUSCH,
transmission time may become longer leading to
increase in power consumption.
Reduction of Transmit Power
Removing the power amplifier stage of an MTC UE is
expected to provide cost benefits.
UL coverage will degrade
Reduction of supported
downlink TM Modes
For rel10 , cat-1 UE’s there are 9 TM modes TM1-TM9.
For IoT, it is limited to TM1 and TM2.
Reduced data rates
For cat0 and cat-m UE’s
For NB-IoT UE’s
Data rate calculation
Data rate =( no. of RB ‘s * no. of subcarriers in an RB * no.
of symbols in a subcarrier * no. of slots * modulation
order ) bits/msec
= 4002 bits/msec
= 4 Mbps
25% of it would be used for control signalling
=> data rate = 1 Mbps.
MCS and TBS
64QAM is not supported for MTC LTE UE’s.
Due to increase in redundacy; code rate, SINR and
efficiency would decrease.
CQI entries with 64QAM are replaced with entries
representing lower SINR.
Minimum TB size is 16bits and max is 680 bits.
Hence, 4 bit MCS table would be sufficient.
Assuming CE level would be changed into a lower one,
UE may report CQI index corresponding to out-of-range,
which may result in no DL PDSCH transmission because
of no matched CQI value with current channel
condition. In this case, we can define CQI indices
representing lower spectral efficiency values, which
avoid the situation what we discussed above.