Philippos Assimakopoulos, Communications Research Group

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 644526 (iCIRRUS)

A 5G FRONTHAUL FOR CONVERGED NETWORKS

Philippos Assimakopoulos, Communications Research Group, University of Kent

CTTE 2015/ COMBO workshop 10th November, 2015, Munich, Germany

The iCIRRUS project

iCIRRUS: intelligent Converged network consolidating Radio and optical access aRound USer equipment http://www.icirrus-5gnet.eu, Facebook, Twitter, Linkedin …. 11-partner Horizon 2020 ICT project in Future Networks theme Start date: 1 January, 2015. 36 months. 3.83 MEuros. Coordinator: UniKent Partners: University of Kent, ADVA Optical Networking, Orange, Telekom Slovenije, Primetel, Wellness Telecom, HHI, University of Essex, JDSU, IAF GmbH, IDCC


http://www.icirrus-5gnet.eu/

The concept

Will discuss some of the details later, but key are: 1. Ethernet in fronthaul 2. Intelligent operation then brought

to fronthaul 3. Added intelligence for D2D and

hetnet operation 4. Centralised functions available to

mobile cloud processing

C-RAN important for 5G D2D, mm-wave, mobile cloud important for 5G


Wireless-fibre communications: C-RAN and the fronthaul

• Require shorter wireless distances for high data-rate services, and so less users are sharing available bandwidth. Two approaches:

• Small co-operating cells or distributed antennas/remote radio heads

• Small cells:

• Mode of operation clearer (scales from current provision). Lots of backhaul links. Co-operation between cells more limited.

• Distributed antennas/remote radio heads:

• Co-operation for beamforming, ICI, coordinated multipoint fundamentally more achievable. C-RAN BBU pooling permits greater network function virtualization. High demands on fibre distribution network.


Challenges for the fronthaul

Current preferred solution is sampled radio waveform transport: CPRI/ORI Specific solution for fronthaul – convergence? TDM streams – how to utilize bandwidth of converged network efficiently? OAM, SON etc…? Bit-rates!

Current CPRI/ORI interfaces Projected requirements Line rate Example Use Possible uses Approx. line rate*

614.4 Mb/s 10 MHz LTE channel, with 8B10B encoding

100 MHz, 8 antennas (sectors/MIMO/CoMP)

28 Gb/s

4.9152 Gb/s 8 x 10MHz (multiple antennas, 8B10B)

500 MHz, 8 antennas (sectors/MIMO/CoMP)

141 Gb/s

10.1376 Gb/s 10 x 20 MHz (multiple antennas, 64B66B)

500 MHz, 16x8 massive MIMO

2.25 Tb/s


Use of Ethernet in the fronthaul

• Use of commodity equipment, or at least lower-cost, industry-standard equipment

• Sharing of equipment with fixed access networks, enabling greater convergence and cost reductions

• Ethernet OAM functions standardised

• Use of switches/routers to enable statistical multiplexing gains and lower the aggregate bit-rate requirements of some links

• Use of standard IP/Ethernet network switching/routing functionality, including moves to functional virtualisation and overall network orchestration

• Monitoring through compatible hardware probes.


BBU pool to RRH connection through switches

Low-latency switching required: Cut-through operation No contention/queuing


What sort of Ethernet links?

• Ethernet over CPRI? Only real advantage is provision of OAM

• CPRI over Ethernet? Possible Loss of synchronism through Ethernet switches Additional framing overhead

• Sample waveform placed directly in Ethernet frames New standards required Loss of synchronism

• Bit-rate/bandwidth requirements

• New standardization efforts: • IEEE 1904.3 (Radio-over-Ethernet)

• 802.1CM – (Time-Sensitive Networking for Fronthaul)


Round-robin transmission with VLANs

• SynchE required • Dedicated VLANs

Carrier aggregation

20 MHz

40 MHz

60 MHz

80 MHz

100 MHz

Max Antenna ports per

100G link, A

98 49 32 24 19


Weaknesses of Ethernet in the fronthaul

• No inherent support for synchronisation Solutions widely adopted:

Synchronous Ethernet (Frequency) IEEE1588-2008 (Phase / Time)

May require new profiles / design rules to meet fronthaul requirements

• Latency (and Latency Variation) Cut-through forwarding? Pre-emption? …

• Does not solve the excessive bit-rate problem


New functional split

New functional split lies between PHY and MAC (orange line) supports:

• SISO (see figure) transport of hard bits in the downlink and hard and soft bits on the uplink

• Massive MIMO by shifting the beamformer into the RRH

• CoMP by including information exchange between adjancent cells over a new X2 interface


Implications of new functional split

• Bit rate reduction and improved network utilisation from statistical multiplexing (bit rates 10x times lower than sampled I/Q)

• Structural convergence, topology and traffic management become more straightforward

• Radio (modulation) “waveform” agnostic • BER: frame loss has different effect than with sampled waveforms (HARQ

with user, not whole radio frame) • Latency and Synchronisation requirements will be different and need

consideration • Modification /extension of some -> to Backhaul interfaces (e.g. some X2

signalling) -> to Remote for some functions • Additional control interfaces may be required – currently embedded within

BBU • OAM and SON functionality


Operation under a new functional split

• Some concepts: • Control process transports control primitives, data process encapsulates LTE MAC TBs • Control information (resource allocation, MCS) need highest protection • SDN-type control for mapper selection • Mappers for CPRI-over-Ethernet, generic I/Q-over-Ethernet, baseband (MAC)-over-Ethernet….. • SON predictive algorithms, variable ETH frame sizes, link utilisation, smart probing


X-haul

• Co-existence with fixed access, PONs (e.g. G.989.x)/ FTTx , CWDM, TDM • Wireless fronthauling/backhauling • Shared infrastructure (OPEX, CAPEX) • Need for advanced network load provisioning and traffic management • Resource pooling and virtualised functions • But…Even pressuming IP traffic (esp. Streaming-type) statistics different from

mobile access.

X-haul

RURU

RU

WD

M

WD

M

SDU

NetworkController /

EvolvedPacket Core

DU

BBU Hotel

DU

DU

Backhaul

DU

RURU

RU

RUDU

DU

RURU

RU

OLT

S

S

ONU

ONU

ONU

RoE mapper

S ETH Switch

Main CO

FTTxFTTcFTThFTTbMDUs


This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 644526 (iCIRRUS)

Summary

• New functional split for fronthaul entities in C-RAN proposed • Alleviates bit-rate requirements • Allows stat mux gains, network load management etc.. • Dyanmic RoE mapper selection with SDN-type control and SON

predictive algorithms.

• Important requirements for latency and synchronisation/jitter remain, if requirements for correct radio frame transmission are to be met

• Synchronous Ethernet, PtP etc., and monitoring of links for QoS required

(OAM and SON functions will be important)

• Ethernet equipment can allow for converged traffic through the x-haul • Traffic management and load provisioning are important • Reduced costs for operators

Bit rates


Channel BW/MHz

IFFT size

Samples per slot3

Sample rate1 /MHz

Data rate2 16-bit (8-

bit)/Mbps 1.4 128 960 1.92 61.44 (30.72) 3 256 1920 3.84 122.88 (61.44) 5 512 3840 7.68 245.76 (122.88)

10 1024 7680 15.36 491.52 (245.76) 20 2048 15360 30.72 983.04 (491.52)

Channel BW/MHz

Sample rate

/MHz

Data rate /Gbps

20 bpS 16 bpS 8 bpS 20 30.72 1.229 0.983 0.492 40 61.44 2.458 1.966 0.983 60 92.16 3.686 2.949 1.475 80 122.88 4.915 3.932 1.966

100 153.6 6.144 4.92 2.458 5G1 1000 40 32 16

Table 2.1. Data rates for LTE system bandwidths per physical antenna port.

1Sample rate= IFFT_size/Ts 2Data rate= sample_rate x 2 x 16 bpS, (factor of 2 for I and Q and 16-bits per sample)

3Samples per slot = Sample_rate/slot_duration

Table 2.2. Data rates for LTE-A and 5G (est.) system bandwidths per physical antenna port for different sample widths.

1Expected for 5G and assuming a bandwidth of 1 GHz and sampling at the Nyquist rate theoretical limit. The bandwidth may come from new spectrum allocations in the form of carrier aggregation or at mm-wave frequencies.

Bit rates


Channel BW/MHz

Sample rate

/MHz

Data rate (16 bpS) /Gbps No. of antennas per sector at RU

2 4 8 16 64 128

20 30.72 1.966 3.932 7.864 15.728 62.912 125.824 40 61.44

3.932 7.864 15.728 31.456 125.824 251.648 60 92.16

5.898 11.796 23.592 47.184 188.736 377.472 80 122.88

7.864 15.728 31.456 62.912 251.648 503.296 100 153.6 9.84 19.68 39.36 78.72 314.88 629.76 5G1 1000 64 128 256 512 2048 4096

Table 2.3. Data rates for LTE-A and 5G (est.) system bandwidths per RU sector for different no. of MIMO antennas (including massive MIMO implementations).

Bit rates


Channel BW/MHz

Sample rate

/MHz

CPRI data rates (15 bpS) /Gbps 1 No. of antennas per sector at RU

1 2 4 8 16 64 128

20 30.72 1.2288 2.4576 4.9152 9.8304 16.2202 64.8806 129.7613

40 61.44 2.4576 4.9152 9.8304 16.2202 32.4403 129.7613 259.5226

80 122.88 4.9152 9.8304 16.2202 32.4403 64.8806 259.5226 519.0451

100 153.6 6.1440 10.1376 20.2752 40.5504 81.1008 324.4032 648.8064

Table 2.4. Extrapolated data rate requirements for CPRI for LTE-A and 5G (est.) system bandwidths per RU sector for different no. of MIMO antennas. Green fonts indicate data rates that are currently supported by CPRI specs while red fonts indicate data rates that will need to be supported in the future.

Documents

Philippos Assimakopoulos, Communications Research Group