Passive xWDM Wireless Fronthaul Basics
2017-10-09
Mobile traffic is booming and this evolution is backed up by both the evolution of 4G and the coming introduction of 5G, which will deliver a downlink user experience of 100Mbps everywhere and 1-10Gbps locally, with a latency of less than 1ms. Such increase in traffic requires Cell Densification and adds changes in to the Mobile Access Network Design. Wireless Fronthaul becomes more popular and one of the most efficient transport methods for Wireless Fronthaul CPRI traffic becomes passive CWDM and DWDM.
 
Demand:
 
During last couple of years mobile traffic have grown significantly and is expected to grow with CAGR of 47% till 2021:
 
 Wireless Fronhaul - Traffic Growth
Figure1: Global Mobile Data Traffic, 2016 to 2021 (Cisco) (Source)
 
Key drivers for such significant growth are:
 
global growth of mobile device and connections (2016-2021 forecasted 8% CAGR)
people habits of using mobile devices have changed
People more and more watch video, listen to audio make video calls. In 2013 on average users watched about two hours of video per month, listened two hours of audio, made five video calls and downloaded two apps over their cellular network, in 2018, it’s expected that average user will watch 20 hours of video per month, listen to 10 hours of video, make 11 video calls and download 20 apps.
 
Top traffic-generating mobile apps on Android: Facebook, YouTube, Netflix,TubeMate, Instagram, TuneIn, SoundCloud, Flipboard, Skype and Twitter.
 
Wireless Frontaul Introduction:
 
As traffic is booming cell densification in traffic heavy areas becomes popular and C-RAN or Wireless Fronthaul (Centralized Radio Access Network) is beginning to gain momentum worldwide with major tier 1 operators including Verizon Communications, AT&T, Sprint, China Mobile, Vodafone, TIM (Telecom Italia Mobile), Orange and Telefonica. Key idea behind C-RAN is that Digital Units (or Baseband Units) are placed at a centralized location, and the Remote Radio Units (RRU’s) are placed at distances up to several kilometers away from the baseband site (<15km due to latency). The connection from a baseband unit to a remote radio unit is typically a fiber facility which is referred to as “wireless fronthaul”. Key advantage for C-RAN are:
 
improved performance (as coordination between cells)
lower power consumption
smaller footprint
potentially lower site lease costs
 
C-RAN and Wireless Fronthaul CPRI Transport:
 
The best facility for CPRI transport in Wireless Fronthaul is dark fiber, because encapsulating CPRI into another protocol introduces too much latency and jitter. Since the monthly lease of a dark fiber pair can be high and several CPRI streams are required, two best options for CPRI transport in modern Wireless Fronthaul Access are Coarse Wave Division Multiplexing (CWDM) and Dense Wave Division Multiplexing (DWDM).
CWDM systems are passive and allow multiple wavelengths to be transported on a single fiber by using matched “colored” SFP’s in the baseband and remote radio end. Up to 16 CPRI wavelengths can be combined on the same fiber using a passive filter.With use of passive DWDM we can have up to 40 CPRI wavelength on same fiber where we can make chain or ring topologies and make „drop and continue” method, where part of wavelengths can be dropped at a site and the rest of the wavelengths continue on to the next site.
 
Passive xWDM has advantage of low cost, low latency, technology requires no power and has the highest reliability thus the solution has many advantages for C-RAN Wireless Fronthaul/CPRI Transport.
 
Fiberland C-RAN/CPRI Wireless Fronthaul Transport Solution:
 
To make xWDM Fronthaul transport for base stations what we need is:
 
1. „Colored” CPRI SFP/SFP+ modules in the baseband and remote radio end. They can either be CWDM or DWDM type depending on total channel amount requirements and as well depending on the speed requirements they can either be: 10GFH modules supporting from CPRI Option 2 (1228.8Mbps) up to CPRI Option 8 (10.138 Gbps) or 2.67G-SFP supporting from CPRI option 1 (614.4Mbps) to CPRI Option 3 (2.458 Gbps). Fiberland CPRI modules can be compatible with all main basestation brands, like Huawei DBS 3900, Ericsson RBS 6000, Nokia Flexi or Nokia AirScale and others.
For more details selecting „colored” CPRI SFP/SFP+ modules please use links below:
 
Supported CPRI/OBSAI Data Rates CPRI option 1 (614.4 Mbps), CPRI option 2 (1228.8 Mbps), CPRI option 3 (2.458 Gbps), OBSAI RP3 x 1 (768 Mbps), OBSAI RP3 x 2 (1.536 Gbps) CPRI option 2 (1228.8 Mbps), CPRI option 3 (2.458 Gbps), CPRI option 5 (4.915 Gbps), CPRI option 6 (6.144 Gbps), CPRI option 7 (9.830 Gbps), CPRI option 8 (10.138 Gbps), OBSAI RP3 x 2 (1.536 Gbps), OBSAI RP3 x 4 (3.072 Gbps), OBSAI RP3 x 8 (6.144 Gbps)
CWDM Link to 2.67G CWDM SFP Link to 10GFH CWDM SFP+
DWDM Link to 2.67G DWDM SFP Link to 10GFH DWDM SFP+
 
2. Passive xWDM mux/demux units Here as well based on the total channel requirements we need to chose between CWDM or DWDM Mux/Demux and as well if we are going to have Single Fiber or Double fiber connections between baseband units and radio units.
For more details selecting passive xWDM Mux/Demux units please use links below:
 
Single Fiber Double Fiber
CWDM Link to SF CWDM Muxes Link to DF CWDM Muxes
DWDM Link to SF DWDM Muxes Link to DF DWDM Muxes
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