Passive xWDM Wireless Fronthaul Basics

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 an increase in traffic requires Cell Densification and adds changes 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 the last couple of years, mobile traffic has grown significantly and is expected to grow with a CAGR of 47% till 2021:

Figure 1: Global Mobile Data Traffic, 2016 to 2021 (Cisco) (Source)

Key drivers for such significant growth are:

• Global growth of mobile devices and connections (2016-2021 forecasted 8% CAGR)
• People's habits of using mobile devices have changed
• People watch videos, listen to audio, and make video calls. In 2013, on average, users watched about two hours of video materials per month, listened to 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 advantages of 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, the 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” SFPs in the baseband and remote radio end. Up to 16 CPRI wavelengths can be combined on the same fiber using a passive filter. With the use of passive DWDM, we can have up to 40 CPRI wavelengths on the same fiber, where we can make chain or ring topologies and use the „drop and continue” method, where part of the wavelengths can be dropped at a site and the rest of the wavelengths continue on to the next site.
Passive xWDM has the advantage of low cost, low latency, requires no power, and has the highest reliability. Thus, the solution has many advantages for C-RAN Wireless Fronthaul/CPRI Transport.

EDGE Optic’s 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 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). EDGE Optic’s CPRI modules can be compatible with all main basestation brands, like Huawei DBS 3900, Ericsson RBS 6000, Nokia Flexi, Nokia AirScale, and others.
For more details, selecting „colored” CPRI SFP/SFP+ modules, please use the links below:

2. Passive xWDM mux/demux units :
Here as well, based on the total channel requirements, we need to choose between CWDM or DWDM Mux/Demux, and whether we are going to have single-fiber or double-fiber connections between baseband units and radio units.
For more details on selecting passive xWDM Mux/Demux units, please use the links below:

If any questions/comments, feel free to write: sales@edgeoptic.com