The document discusses mobile network technologies, focusing on fronthaul, backhaul, and radio unit configurations, as well as advancements in LTE-A such as carrier aggregation and MIMO. It highlights various transport options for CPRI and the advantages and challenges of using Ethernet in fronthaul applications. Key considerations include bandwidth predictions, synchronization requirements, and future developments in mobile technology architecture.

1. Mobile Fronthaul
Piotr Gruszczyński
next Generation Technologies
pg@nextgt.com

2. next Generation Technologies – consultancy

3. Mobile Network
Service: HLR/HSS, MSC, S/GGSN, MME, SGw,PGw,CSCF…
Radio: BSC, RNC
Base Stations: GSM BTS, NodeB, eNodeB

4. Mobile Backhaul
Physical
radio lines (microwave)
E1 over copper
optical fiber
Data
TDM
ATM
Ethernet
Management
Carrier/Metro Ethernet
IP/MPLS

5. Base station basics
Radio unit (RU), radio head (RH)
sends and receives radio data to and
from antenna
e.g. RUG, Radio Unit GSM
Base Band unit (BBU)
digital unit for decoding or encoding
radio data
e.g. DUW,Digital Unit for WCDMA
RF cable
the longer the bigger power loss

6. Fiber-to-the-Antenna
Remote radio unit (RRU), remote
radio head (RH)
stays where it was
Base Band unit (BBU)
co-located in a “baseband hotel”
Optical fiber
designed for up to 10km
works fine within 40km

7. Fronthaul was born
Optical distribution network
Number of base station sites (for BBU housing) can be
reduced by factor of 10
Needed some standardisation

8. RAN Architectures options
Distributed RAN
BBUs serve (tens of) RRUs – local as well as remote
Centralized RAN (C-RAN 1)
BBUs serve (tens of) RRUs – remote
Cloud RAN (C-RAN 2)
potentially hundreds of RRUs share the same pool of BBUs
Virtualised RAN
BBU is built as virtualised network function (VNF)
on commercial-off-the-shelf (COTS) hardware

9. CPRI
Common Public Radio Interface
vendor initiative to implement FttA,
adopted by ETSI as ORI, Open Radio Interface.
Serial data link
Specification only of the lower layers (1&2) of OSI model.
Generic enough to suit
scalable rates,
physical access medium type,
and air interface.
Fiber link important replacement for coax.

10. Current transport
20 MHz RF bandwidth
maximum single carrier for LTE at the moment
~1Gb/s data bandwidth for I/Q data transmission per Antenna Carrier
The bit speed of the CPRI link is a multiple of BaseBand Clock
40 x 30,72MHz = 1.23 Gbit/s
80 x 30,72MHz = 2.46 Gbit/s
160 x 30.72MHz= 4.91 Gbit/s
320 x 30.72MHz= 9.82 Gbit/s [300/75 Mbit/s LTE]
Without any further development we are limited to:
distance of 10km
5 microseconds of delay per km, 50-70 microseconds for RRU

11. I’m not impressed

12. LTE-A from 3GPP Release 10 (1)
Carrier Aggregation
ability to aggregate up to five 20 MHz carriers from a variety
of different spectrum bands
as well as a combination of frequency-division duplex (FDD) and
time-division duplex (TDD) modes
this enables very high throughput bursts without requiring
contiguous frequency bands.
High-Order MIMO
provides up to 8x downlink multiple input/output (MIMO)
and 4 uplink MIMO for higher peak data rates
massive MIMO in future.

13. LTE-A from 3GPP Release 10 (2)
Enhanced Inter-Cell Interference Coordination (eICIC)
designed to enable better management of interference between
layers in heterogeneous networks (HetNets)
macro, micro and small cell layer
using and reusing some of the same frequencies.
Coordinated Multi-Point transmission and scheduling
send on the uplink,
CoMP selects and combines signals from as many as 8
eNodeB’s
to improve cell edge throughput and performance, typically in
HetNet environment including small cells

14. Bandwidth predictions
ORI projected requirements for bandwidth
100 MHz, 8 antennas (sectors/MIMO/CoMP): 28 Gb/s
500 MHz, 8 antennas (sectors/MIMO/CoMP): 141 Gb/s
...
500 MHz, 16x8, massive MIMO: 2.25 Tb/s

15. Time Sync Delivery Requirement
Air interface requirements, less:
150ns for base station internal tolerances
250ns for short term holdover (e.g. to allow reference switch)
Example for LTE TDD (overlapping coverage):
±1.5 s at the air interfaceμ
±1.1 s at th network interfaceμ
Example for LTE CoMP (tightest tolerance):
± 500ns at the air interface
± 350ns at the network interface (no reference switching)

16. CPRI Transport Options
Microwave
E-band radio
Dedicated fiber
Optical Transport Network
Passive Optical Network
Wavelength-Division Multiplexing – Dense, Coarse
Carrier/Metro Ethernet

17. CPRI Transport Options
Wavelength-based systems offers a good combination of
characteristics for CPRI transport:
in particular,Coarse Wavelength-Division Multiplexing (CWDM)
supports low propagation delays and high data throughout,
while being an economical choice
in equipment costs – purely passive, good MTBF
In use of fiber resources - low power and space consumption
WDM disadvantages:
no standard optical surveillance
no standard performance monitoring available (SLA)
usage of tunable SFP+ and XFP may not be possible

18. Ethernet in fronthaul – advantages
Use of commodity equipment, or lower-cost, industry-
standard equipment.
Sharing of equipment with fixed access networks.
Ethernet OAM functions are 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 over all network orchestration.
Monitoring through compatible hardware probes.

19. Ethernet in fronthaul - challenges
Does not solve fundamental bit rate problem.
Destroys synchronisation, timing inherent in a TDM stream.
Aggregation, switching units make timing problems worse
(queuing, contention…)
store-and-forward adds latency (1-8 μs)
cut-thru makes aggregation difficult if not impossible

20. Time Sensitive Networks – Ethernet
802.1Qbu
Preemption (collaborating w/ 802.3br Interspersing Express Traffic)
Allow time sensitive frames to preempt other frames
802.1Qbv
Time Aware Shaper (TAS) -- Scheduled Traffic
Adds windows where non-scheduled traffic is blocked to ensure
lowest latency
802.1Qcc
Stream Reservation Protocol Gen 1.1 (SRP Enhancements and
Performance Improvements)
Bandwidth and latency reservations to avoid time-sensitive queues
to overflow and drop packets

21. Synchronisation options
Enhanced SyncE
G.8262.1, revised G.8271.1
Enhanced PRTC (G.8272.1): +/- 30 ns
Targeting applications in the 100 ns range
802.1 AS (gPTP), 802.1 AS-REV
IEEE 1588v2 Precision Time Protocol Ethernet specific profile
takes fronthaul requirements into account

22. Maybe new fronthaul?
Redefinition of splitting point between BBU and RRH
Drastically reduced optical bandwidth can be achieved.
Optical traffic is proportional to mobile traffic.
Variable bit rate
Functionality of mobile systems (e.g. C-RAN, CoMP) should
be kept
Latency requirement is the same (HARQ)

23. Conclusions and questions
Piotr Gruszczyński
pg@nextgt.com