Sounds like LTE!Instructor: Jakub Bluszcz+48 607 221 954e-mail: jakub.bluszcz@leliwa.com

Leliwa Sp. z o.o.www.leliwa.com

Sounds like LTE!Topics:

Mobile Network EvolutionIncrease of Throughput:Changes in symbol rateMultiple accessChannel bandwidth and filtersMIMOArchitectureShort Data StructuresLocation UpdateSelf-configuration and Self-optimization

Mobile Network Evolution

3GPP mobile systems20102009200820072006200520042003200220012000199919981997199619951994199319921991 GSM GPRS EDGE evolved EDGE UMTS HSDPA HSUPA evolved HSPA LTE/EPS9.6k1.9M2.0M42M173M326MGSMUMTSLTE

Changes in Symbol Rate

GSM / GPRS / EDGEGSM is like a pianist who plays allegro (i.e. cheerful, brisk etc.*)*modulation symbol rate 270 ksps

UMTS / HSDPA / HSUPAUMTS is like a pianist who plays prestissimo (extremely fast*)* modulation symbol rate 3,84 Msps (14 times faster than GSM)

LTELTE is like a pianist who plays largo (very slow tempo*).* modulation symbol rate 15 ksps (18 times slower than GSM)

ConclusionUp to now the common method to increase throughput was to increase the modulation symbol rateIn LTE the increase of throughput is achieved by other means.

What is the benefit of decreased symbol rate?

Multipath propagation

Multipath propagation

Inter-Symbol Interference (ISI)

Inter-Symbol InterferenceIn the high-symbol rate systems even very low relative delays of multipath propagation components cause multi-symbol offsets between paths. This makes the proper detection of the signal difficult.

Inter-Symbol InterferenceRake receivers are commonly used to minimise the impact of Inter-Symbol Interference.The Rake receiver requires vast amount of fast memory, processing power and energy.

Rake receiverThe complexity of rake receiver increases along with the symbol rate.

Inter-Symbol InterferenceIn the low symbol-rate systems (e.g. LTE) even large differences in multipath length cause only small relative symbol offset causing Inter-Symbol Interference just at the boundary between two consecutive symbols, while keeping the rest of symbol intact.

Inter-Symbol InterferenceLTE receiver neglects initial part of the symbol and only interference-free part of the symbol is being processed.

Multiple access

1G FDMA (e.g. NMT) (Frequency Division Multiple Access)timefrequencyf1f2f3f4f5f6f7

1G FDMAFDMA is like a piano where a different pianist plays on each octave.

2G TDMA (e.g. GSM) (Time Division Multiple Access)timefrequencytime slot1time slot2time slot3time slot4

2G TDMATDMA is like a piano in front of which a pianist changes after playing just a few bars.

3G CDMA (e.g. UMTS)(Code Division Multiple Access)frequencytimecodecode1code2code3code4

3G CDMACDMA is like an orchestra where each musician can utilise the full scale of his/her instrument but to avoid mutual disturbance they all must be controlled by a single conductor.

Single-carrier systemNMT (1G), GSM (2G), UMTS (3G) are the examples of single-carrier modulation systems.It means, in the musical analogy, that the pianist plays with one finger, being able to get only one sound at a time (i.e. plays melodically).

4G OFDMA (e.g. LTE) (Orthogonal Frequency Division Multiple Access)

Multi-carrier systemLTE and OFDMA are the examples of multi-carrier systems (max. 1200).It means, in the musical analogy, that the pianist plays using all his/her fingers being able to get more than one sound concurrently (i.e. plays harmonically).

Single- and Multi-carrier systemConclusion:Though the sound lasts longer, the number of played sounds can be still high if they are played simultaneously.

OFDMAIn the LTE R8/R9 the maximum number of sub-carriers (frequency sub-channels) is 1200.It means, in the musical analogy, that the piano is replaced by the instrument having much wider scale and number of keys (e.g. organ).

OFDMAThe scale of an instrument can be divided into groups of octaves that are assigned to different organists.

Channel bandwidth and filters

Fourier transform

Fourier transformtttFFFfff

Fourier transform4 kHz tone transmitted continuously 4 kHz tone transmitted cyclically:

transmit time = 0.001s, pause time = 0.001sHuman hears Fourier transform of an acoustic signal (hair cells in consecutive cochlea parts are sensitive for consecutive frequency bands).These are two different sounds for the human hence their Fourier transforms are different as well.

Fourier transformtFf

Filtering f

Filtering fbandwidth required for proper signal detection in traditional receiver

FDMA and OFDMA filteringfFDMAfOFDMA

Channel widthFtFtffchannel widthchannel width

Channel/subchannel width5 MHz3840 kspsUMTS15 kHz15 kspsLTE200 kHz270 kspsGSMChannel widthSymbol rateSystem

Fourier transformtFf66.6 s (1/15 kHz) 15 kHz15 kHz15 kHz15 kHz15 kHz15 kHz15 kHz15 kHz15 kHz15 kHz

OFDMA

MIMO

MIMO (LTE, HSPA+)LRMIMO is like a stereo sound...

MIMO (2x2)TxRxMIMO 2x2 allows to nearly double the throughput in extremely favourable conditions.

MIMO efficiencyIf the MIMO propagation paths are fully independent the system reaches its maximum efficiency (i.e. throughput is nearly doubled for 2x2 MIMO or quadrupled for 4x4 MIMO).

MIMO efficiencyOn the other hand, fully dependent MIMO propagation paths are not increasing throughput at all.

Bitrates in LTE

Architecture

UMTS PS Architecture step 1 R99 ArchitectureNBRNCSGSNGGSNIP

UMTS PS Architecture step 2 R7 Architecture (optional)NBSGSNGGSNIP

EPS/LTE ArchitectureeNBS-GWP-GWIPMME

GERAN/UTRAN R99 ArchitectureNB/BTSRNC/BSCSGSNanalysis and decisionsRelatively long adaptation time to changing radio conditions

UTRAN (HSPA) ArchitectureNB/BTSRNC/BSCSGSNanalysis and decisions (R99)Shorter adaptation time to changing radio conditions for HSPA servicesanalysis and decisions (HSPA)

E-UTRAN (LTE) ArchitectureeNBS-GWShorter adaptation time to changing radio conditionsanalysis and decisionsMME

Short Data Structures

Data structures UMTS R99:10/20/40/80 ms UMTS (HSDPA):2 msLTE:1msTTI

Code redundancy (protection)

Long data structure (step 1)

Long data structure (step 2)

Long data structure (step 3)It was possible to send more data.

Short data structures

Packetisation delay

Packetisation delay

Delays:UEeNode B1 ms1.5 ms1 ms1 ms1 ms1.5 msTTI + frame alignmentHARQ RTT 5 ms** For reference: HSDPA HARQ RTT 12ms, HSUPA HARQ RTT 40ms (min 16ms)

Location Update

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GSM/UMTS location updateSGSN

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GSM/UMTS location updateSGSN

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GSM/UMTS - pagingSGSN

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GSM/UMTS - pagingSGSN

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GSM/UMTS loc. upd. & packet transferSGSN

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GSM/UMTS loc. upd. & packet transferSGSNTransmission gap from 5 to 15s

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LTE registration 123456789101112131415161718192021222324252627282930313233343536MMES-GW

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LTE location update & packet transfer123456789101112131415161718192021222324252627282930313233343536MMES-GW

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LTE location update & packet transfer123456789101112131415161718192021222324252627282930313233343536MMES-GW

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LTE location update & packet transfer123456789101112131415161718192021222324252627282930313233343536MMES-GW

Self-configuration and optimisationEach cell of the system is configured by several thousands of parameters defined manually and being constantly optimised.In the future LTE networks most of the parameters will be configured automatically (including key parameters like: power, frequency allocation or antenna direction).

Thank you for your attention