rmcs_lecture 7 v12_1_annotated.pdf

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Version 12.1, D.M.Lauder Page 1 University Of Hertfordshire 2012

7 3G High Speed Packet Access and 3G/4G Long TermEvolution (3G UMTS HSPA, 3G LTE & 4G LTE)

7.1 Development of 3G High Speed Packet Ac cess (HSPA)

3GPP Releases 4 - 8 added various capabilities including:

High Speed Downlink Packet Access, HSDPA

High Speed Uplink Packet Access, HSUPA

High Speed Packet Access Evolution, HSPA+

7.1.1 3G HSPA

3G HSPA extends UMTS or W-CDMA to increase data transfer speeds. It usesdifferent techniques for the downlink and uplink.

The original 3GPP Release 99 was primarily designed for circuit-switched operationand was not well suited to packet-switched operation. The maximum download datarate was 384 kbps.

3G HSPA was developed to support packet-switched operation and higher data rates,to support new non-voice services and to compete with fixed line broadband services.In addition to increased data transfer rates, 3G UMTS HSPA offers other benefitsincluding:

Use of higher order modulation: 16QAM is used in the downlink instead ofQPSK to increase data rate. This provides 'raw' downlink data rates of 14Mbps. QPSK is still used in the uplink and provides 'raw' uplink data rates of upto 5.8 Mbps (i.e. data rates over the radio channel, not including protocoloverheads).

Shorter Transmission Time Interval (TTI): This reduces the round trip time andreduces latency.

Shared channel transmission: Efficiency is increased by sharing resources.

Link adaptation: Maximises channel usage.

Fast Node B scheduling: With adaptive coding and modulation for thedownlink. This adapts to varying radio channel and interference conditions. Italso accommodates 'bursty' data traffic.

Node B based Hybrid ARQ: A retransmission technique that reduces roundtrip times and uses 'soft combining' of retransmissions to make the systemmore robust.


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7.1.2 HSPA+

HSPA+ or Evolved HSPA includes high order modulation and MIMO (multiple input,multiple output) techniques. For each RF carrier occupying 5MHz bandwidth, it canprovide downlink data rates up to 42 Mbps and uplink data rates up to 11 Mbps.

7.2 3G Long Term Evolu tion (LTE)

Whereas UMTS, HSPA and HSPA+ use a W-CDMA 'air interface', LTE uses acompletely new 'air interface' and provides evolution beyond HSPA+ with higher datatraffic rates.

LTE uses OFDMA/SC-FDMA rather than CDMA and LTE is also the basis for 4Gsystems.

Whereas HSPA+ can provide 'raw' downlink and uplink data rates of 42 Mbps and11 Mbps respectively, 3G LTE can provide 'raw' downlink and uplink data rates of100 Mbps and 50 Mbps respectively.

Latency (round trip times) are also reduced from approx. 150 ms with UMTS W-CDMAand approx 50ms (max) with HSPA+ to approx 10 ms with 3G LTE.

7.2.1 Summary of 3G LTE parameters

Data connection type: All-IP network supporting IPv4 and IPv6 but not circuit-

switched voice calls. Voice calls can be carried as Voiceover IP (VoIP) however.

Peak 'raw' downlink data rates (using 64QAM): SISO: 100 Mbps,2x2 MIMO: 172 Mbps,4x4 MIMO: 326 Mbps

Peak 'raw' uplink data rates: QPSK: 50 Mbps, 16QAM: 57 Mbps, 64QAM: 86 Mbps.

RF Channel bandwidths: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz.

Duplexing schemes: FDD & TDD

Speed of mobile users: 0 - 15 km/h (optimised), 15 - 120 km/h (highperformance)Why is speed significant?

Latency Active in less than 100ms from idle, small packet latencyapprox. 10 ms

Spectral efficiency Downlink: 3 - 4 times higher than HSDPA 3G PPRelease 6Uplink: 2 -3 times higher than HSUPA 3G PP Release 6

Multiple Access schemes OFDMA (Downlink), SC-FDMA (Uplink)

Modulation types QPSK, 16QAM, 64QAM (Uplink and downlink)


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7.2.2 Modulation Types for 3G LTE

7.2.2.1 LTE OFDM and OFDMA

OFDM is Orthogonal Frequency Division Multiplex. This is used as the signal bearer inLTE. OFDM is also used in some Wireless LANs (WLAN), WiMAX, Digital VideoBroadcasting (DVB) and Digital Audio Broadcasting (DAB). The DMT modulation usedin ADSL and VDSL wire line communication is a variant of OFDM.

OFDM is resistant to multipath fading and interference and modulation/demodulationcan be performed using digital signal processing techniques.

In LTE, the OFDM uses a maximum of 2048 (2 K) sub-carriers with a spacing of15 kHz. Due to the nature of OFDM, the symbol period for each sub-carrier is 1/(15 x103) (in general, 1/[sub-carrier spacing])

All mobiles can receive all 2048 sub-carriers but a base station may not transmit themall. A base station transmits at least 72 sub-carriers (6 Resource Blocks where aResource Block consists of 12 sub-carriers) This allows mobiles to communicate withmultiple base stations simultaneously.

The OFDM signal can use three types of modulation for each OFDM sub-carrier:

QPSK/4QAM, 2 bits per symbol

16QAM, 4 bits per symbol

64QAM, 6 bits per symbol.

OFDMA is Orthogonal Frequency Division Multiple Access which is an access schemeassociated with OFDM that is used in the downlink. OFDMA is a multi-user version ofthe OFDM digital modulation scheme. Multiple access is achieved in OFDMA byassigning subsets of subcarriers to individual users. This allows simultaneous low datarate transmission from several users.

'

Outline of OFDMA (to be drawn in lecture)


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7.2.3 LTE SC-FDMA

SC-FDMA is Single Carrier Frequency Division Multiple Access. This accesstechnique is used for the LTE uplink. It is a hybrid format related to OFDMA but SC-FDMA is transmitted by mobiles to overcome the high peak to mean power ratio ofOFDM. This allows RF power amplifiers to be more efficient and hence improvesbattery life.

7.2.4 MIMO

Multiple Input Multiple Output (MIMO) uses multiple antennas at the transmitter andreceiver to enable a variety of signal paths to carry the data. MIMO can chooseseparate paths for each antenna to enable multiple signal paths to be used.MIMO wireless systems use space-time signal processing. Whereas multiple pathsintroduce interference in conventional wireless systems, these additional paths can beused to advantage with MIMO.

General Outline of a MIMO system (to be drawn in lecture)

7.3 4G LTE Ad vanc ed

4G LTE Advanced can provide 'raw' downlink and uplink data rates of 1 Gbps and500 Mbps respectively, with lower latency than 3G LTE. It also includes various newand advanced techniques including:

4G LTE Carrier Aggregation

4G LTE Co-ordinated Multipoint (CoMP)

4G LTE Advanced Relay

4G LTE Device to Device, D2D


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7.3.1 Carrier Aggregation

The target figure for 'raw' downlink data throughput is 1 Gbps for 4G LTE Advanced.Nevertheless, the RF bandwidth of some of the new LTE spectrum allocations isrelatively small, such as 10 - 20MHz bandwidth.

Even where wider bandwidth is available, the maximum RF bandwidth used by asingle 4G LTE Advanced channel is 20 MHz. Even with advances in modulationformats and transmission techniques, a single 20 MHz wide RF channel cannot carrythe maximum data rates specified.

'Carrier Aggregation' (CA) can be used to increase data throughput in 4G LTE Advanced transmission. With Carrier Aggregation, more than one RF carrier is usedsimultaneously. This increases the overall transmission bandwidth and also the datarate compared to a single carrier.

Carrier Aggregation may be within the same band (intra-band) or between twodifferent bands (inter-band). The following types of CA are possible:

7.3.1.1 Intra-band Contiguous.

For Intra-band contiguous carrier aggregation, the carriers are adjacent to each otherin the same band.

The aggregated channel can be considered by the terminal as a single enlarged RFchannel. Hence only one transceiver is required within the terminal or UE.

7.3.1.2 Intra-band Non-Contiguous


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For Intra-band non-contiguous carrier aggregation the carriers are in the same bandbut are not adjacent. Hence the terminal or UE requires a separate transceiver foreach channel.

7.3.1.3 Inter-band Non-Contiguous

For Inter-band non-contiguous carrier aggregation the carriers are in different bands.Hence the terminal or UE requires a separate transceiver for each channel.

7.3.2 Frequency allocations for 4G

There are various possible current and future frequency allocations for 4G in the UK,as shown below:

Fig 7.3.2.1 Overview of bands potentially suitable for mobile broadband in the UKaccording to Ofcom [1]

In the UK, Ofcom has issued a statement on "Securing long term benefits from scarcelow frequency spectrum - UHF strategy statement". The term 'low frequency' in thiscontext means lower than existing UHF mobile allocations such as GSM-900. Inparticular, an 800 MHz allocation has recently been made available for 4G in the UK.

There is also a new allocation for 4G at 2600 MHz and there is further scope for 4G inexisting GSM and UMTS bands by so-called 're-farming'


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In addition to the above bands, there is also a 700MHz band that can already be usedfor mobile broadband in other ITU Regions:

In North and South America (ITU Region 2), the 700 MHz band has alreadybeen allocated to mobile broadband.

In the Asia Pacific region (ITU Region 3), the 700 MHz band has already beenallocated to mobile broadband of is in the process of being allocated, e.g.

Japan Australia and New Zealand.

For ITU Region 1 (Europe, Middle East and Africa), a resolution passed at the 2012World Radio Conference (WRC 12) makes provision for a possible future a decision toallow the 700MHz band to be used for mobile broadband services This future decisionmay be taken at the next World Radio Conference in 2015 (WRC 15).

Why is the use of frequencies such as 800 MHz and 700 MHz particularlyattractive for 4G mobile broadband compared to higher frequencies?

What other services use these frequencies or adjacent frequencies and whatare the consequences of this?

Fig 7.3.2.3 UHF bands IV and V and the proposed 700 MHz band according to Ofcom[1]

With the change to digital terrestrial TV broadcasting in the UK, part of UHF TV Bandhas been cleared of TV broadcasts (channels E61 to E68). This range will be used inUK for 800 MHz mobile broadband from 2013 onwards.

Some users of digital terrestrial TV have broadband UHF pre-amplifiers that are

designed to amplify the whole UHF TV band 470 –

860 MHz. These could be:


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In some types of 'Freeview' DTTV receiver boxes

An pre-amplifier behind the TV set or an indoor TV antenna with built-in pre-amplifier

A pre-amplifier in the loft or a 'mast head' pre-amplifier (in weak signal areas)

Such pre-amplifiers were not designed to handle strong signals from 4G LTE basestations or mobiles within the UHF TV band 470 - 860 MHz and such strong signalsmay cause non-linear effects such as gain compression and intermodulation. Thiscould prevent DTTV signals from being received unless a filter is fitted at the input ofthe pre-amplifier to reject the 4G signals.

7.3.3 Voice calls on 4G

LTE is a purely IP network, so circuit-switched voice calls need to carried using voice-

over-IP (VoIP). There is a standard for this, Voice over LTE (VoLTE) but not allnetwork operators are using VoLTE.

Where VoLTE is not implemented, voice calls can be handled by dropping them onto3G or even 2G networks. This is called Circuit Switched Fall Back (CSFB), and it isspecified in the 3GPP standard for 3G networks.

References

[1] Ofcom Report, Securing long term benefits from scarce low frequency spectrum -UHF strategy statement"Publication date: 16 November 2012

http://stakeholders.ofcom.org.uk/binaries/consultations/uhf-strategy/statement/UHF_statement.pdf

Bibliography

RadioElectronics.com Cellular Telecommunications and Cell Phone TechnologyPageshttp://radio-electronics.com/info/cellulartelecomms/index.php Update dates not available. Accessed Nov 2012

The Register, UK online news web site about Information Technology andTelecommunications that presents an alternative and sometimes critical view.http://www.theregister.co.uk
http://stakeholders.ofcom.org.uk/binaries/consultations/uhf-strategy/statement/UHF_statement.pdfhttp://stakeholders.ofcom.org.uk/binaries/consultations/uhf-strategy/statement/UHF_statement.pdfhttp://stakeholders.ofcom.org.uk/binaries/consultations/uhf-strategy/statement/UHF_statement.pdfhttp://radio-electronics.com/info/cellulartelecomms/index.phphttp://radio-electronics.com/info/cellulartelecomms/index.phphttp://www.theregister.co.uk/http://www.theregister.co.uk/http://www.theregister.co.uk/http://radio-electronics.com/info/cellulartelecomms/index.phphttp://stakeholders.ofcom.org.uk/binaries/consultations/uhf-strategy/statement/UHF_statement.pdfhttp://stakeholders.ofcom.org.uk/binaries/consultations/uhf-strategy/statement/UHF_statement.pdf

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