LTEAirInterface2.ppt

Welcome to the Directed Remote Learning session of

LTE Air Interface Basics

During this course, we will:

• Compare the LTE air interface in terms of Frequency and Time with GSM and UMTS

• Compare the capacity of the LTE air interface with GSM and UMTS

In GSM, the Radio Network portion of the mobile telephone network is called the BSS (Base Station Subsystem).

2G (GSM) and 2.5G (GERAN)

It contains:

BTS BSC

BTS

BTS

TRC To Core

• BTSs (Base Transceiver Stations)

• BSCs (Base Station Controllers)

• TRCs (TRanscoder Controllers)

BSS

3G UMTS/WDMA

It contained:

RNC

Node-B

To Core

• Node-Bs

• RNCs (Radio Network Controllers)

In UMTS, the Radio Network portion is called the UTRAN or, more simply, the RAN (Radio Access Network).

Node-B

Node-B

RAN

4G (almost) EPS

It contains:e-Node B

To Core

• eNBs

In EPS (Evolved Packet System), the Radio Network portion is called the e-UTRAN (where e stands for ‘evolved’) or LTE (Long Term Evolution).

e-Node B

e-node B

LTE or e-UTRAN

Time DomainAll three technologies utilize Time Slots (TSs)

GSM

WCDMA

LTE

667 μsec

577 μsec

500 μsec

Drawings not to scale.

Frames - GSMIn GSM, there are 8 TSs in a frame. Normally, each connection gets its own TS on a carrier of 200KHz

1 frame = 8 TSs4.616 ms

Carrier 1

Carrier 2

Frames - UMTSIn UMTS, there are 15 TSs in a frame. Everyone has a connection on every TS.There is a single carrier having a bandwidth of 5 MHz

1 frame = 15 TSs1 msec

Carrier 1

Frames – LTEIn LTE, two TSs make a subframe and 10 subframes make a frame.

1 frame = 10 Subframes = 20 TSs10 msec

TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS

10

Subframe

987654321

TS



TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS

Subframe

The minimum allocation for a connection is one subframe. Both TSs must be allocated.

10987654321




Subframe

A connection may use several subframes

during a frame.

10987654321




Subframe

Not all subframes have to be allocated

10987654321

1. How many subframes can be transmitted in a second?

Exercise

Frequency – GSM and UMTS

In GSM and UMTS, a subscriber is limited to using a single carrier at any point in time.

Carrier 1

Carrier 2

X

Frequency – LTE 2TSs1 subframe

1 msec

Frequency Block 12 subcarriers @ 15 kHz each

In LTE, the smallest possible frequency allocation is a Frequency Block

A Frequency Block consists of 12 contiguous subcarriers at15 kHz each

freq

Frequency – LTE

A subscriber may be allocated more than one Frequency Block during a subframe*

2TSs1 subframe

1 msec




freq

Frequency – LTE

A subscriber may be allocated more than one Frequency Block during a subframe*

2TSs1 subframe

1 msec




freq

*On the UL, the Frequency Blocks for a single connection must be contiguous. On the DL, they do not have to be contiguous

Frequency – LTE 2TSs1 subframe

1 msec

Not all Frequency Blockshave to be allocated.




freq

2. What is the bandwidth of a Frequency Block? How does this compare with a single GSM carrier? How does this compare with a UMTS carrier?

Exercise

Operator Spectrum

freq

An operator has flexibility in how much spectrum they can allocate for LTE.

Possible allocations are:• 1.4 MHz• 3 MHz• 5 MHz• 10 MHz• 15 MHz• 20 MHz

1.43

5

10

15

20

3. Calculate the number of Frequency Blocks in each allocation that an operator is allowed to use (i.e., 1.4, 3, 5, 10, 15 and 20 MHz). In each case, round down and remove one Frequency Block for guard band purposes.

Exercise

Scheduling Block – LTEIn LTE, the smallest possible allocation for a connection is a Scheduling Block

Frequency Block 12 contiguous subcarriers@ 15 kHz each

2 TSs = 1 subframe = 1 msec

Subcarrier 1Subcarrier 2Subcarrier 3Subcarrier 4Subcarrier 5Subcarrier 6Subcarrier 7Subcarrier 8Subcarrier 9

Subcarrier 10Subcarrier 11Subcarrier 12

Subcarrier 1Subcarrier 2Subcarrier 3Subcarrier 4Subcarrier 5Subcarrier 6Subcarrier 7Subcarrier 8Subcarrier 9

Subcarrier 10Subcarrier 11Subcarrier 12

time

freq

Each subcarrier is 15kHz wide

`

A Scheduling Block consists of :• 1 Frequency Block• 1 subframe

Frequency – LTEA possible allocation for 4 subscribers over 5 subframes

time

freq

2 TSs = 1 subframe = 1 msec


Subscriber 1

SchedulingBlock

Subscriber 2

Subscriber 3Subscriber 4

Unallocated

A closer look at a Time Slot

12 subcarriers Frequency Block

1 Timeslot = 1/2 subframe = 0.5 msec

time

freq

Symbol 1 Symbol 2 Symbol 3 Symbol 4 Symbol 5 Symbol 6 Symbol 7

A Time Slot on one SubCarrier has 7 Resource Elements Each Resource Element carries one symbol (see next slide)

Resource Elements

12 subcarriers Frequency Block

1 msec = 1 subframe = 2 TSs

time

freq

The smallest unit of data transmission is a Resource Element

SchedulingBlock

It consists of:• 1 symbol on• 1 subcarrier

4. How many Resource Elements are in a Scheduling Block?5. For a single Frequency Block, how many Resource Elements can be transmitted in one

second?

Exercise

Bit Rates and Modulation

Symbol1

A symbol (can carry:• 2 bits (if the modulation is QPSK) or• 4 bits (if the modulation is 16QAM) or• 6 bits (if the modulation is 64QAM)

Symbol2

Symbol3

Symbol4

Symbol5

Symbol6

Symbol7

Symbol8

Symbol9

Symbol10

Symbol11

Symbol12

Symbol13

Symbol14

1 msec = 1 subframe = 2 TSs

One subcarrier

6. If QPSK is used, how many bits per second can be transmitted on a single Frequency Block? 7. If 16QAM is used, how many bits per second can be transmitted on a single Frequency Block? 8. If 64QAM is used, how many bits per second can be transmitted on a single Frequency Block? 9. The highest bit-rate possible with EDGE in GSM is approximately 60 kbits/sec per TS. Using all

8 TSs, what bit-rate could EDGE achieve for a single carrier? How does this compare with the three bit-rates of a single Frequency Block on EPS-LTE?

10. Using your answer from question 3, what bit rate could EPS-LTE achieve with 5 MHz of bandwidth using QPSK? Using 16QAM? Using 64QAM?

11. A single DL carrier in UMTS (P5) can achieve a bit-rate of approximately 14 Mbits/sec. Using your answer from question 10, how do the 3 bit-rates compare with the bit-rate of UMTS?

12. A voice call, including all error-coding and signaling, requires approximately 33 kbits/sec to support. Approximately how many voice calls could be supported on a single Frequency Block in EPS-LTE? Assume QPSK modulation.

13. How does the answer in question 12 compare with the number of voice calls supported by a single GSM carrier?

14. How many voice calls could be supported with 5 MHz of bandwidth in EPS-LTE? How does that compare with UMTS?

Exercise

LTEAirInterface2.ppt

Documents

Transcript of LTEAirInterface2.ppt