If you’re a network operator or a service provider, you know that the speed at which data, voice and video traffic is growing will soon swamp your existing network resources. To support that demand, and to continue to grow the network in an efficient way, you must find solutions for preserving spectrum and providing good quality of experience for the end user. But you also know that 5G isn’t far off, so it’s critical to future-proof the network investments you make today.

Given the long investment cycles in mobile, how do operators future-proof their businesses on the way to 5G? They can start by modernizing and reducing costs with centralization, virtualization and consolidation.

Start by Moving to Open and Virtualized Platforms

Many operators are exploring Centralized RAN (C-RAN) architectures as a way to reduce CapEx and OpEx. By centralizing the baseband unit (BBU) and associated cell site routers deeper into the network, space, power and air conditioning expenses can be reduced at the cell tower, and pooled more efficiently in the central office/first aggregation point. Furthermore, operational costs to maintain BBUs and the like can be reduced due to centralization.

Mobile fronthaul is a supporting technology for C-RAN that extends the common public radio interface (CPRI) or Open Base Station Architecture Initiative (OBSAI) connection that already exists between the antenna and the BBU. It can reach a greater distance, often up to 20km. While this reduces operational expenses it does not come without some investment. The following diagram shows how this might look:

Now is a good time to lay additional fiber to the radio site to support today’s growing traffic levels with room to spare for 5G. Where fibers are scarce or it’s too expensive to lay more, solutions like wavelength-division multiplexing (WDM) can knit a number of optical carrier signals onto a single fiber. This technique enables bi-directional communications over each fiber and multiplies capacity.

Another beneficial step for today, that becomes even more important for 5G, is deploying a proactive fiber monitoring system that can detect breakage, connection issues and other faults immediately. Solutions that automatically find and report issues are key to smooth and assured connectivity and they offer quick return on investment when downtime equals lost service revenue.

Fronthaul over CPRI/OBSAI data rates are much higher than backhaul rates due to a number of factors. These include transmission from BBU to multiple remote radio heads (RRH) and the number of bits per sample needed to provide a reliable reconstruction of the air interface when processed by the RRH. In addition, increased distance between the BBU and the end user (cell phone) creates a latency/delay impact on the round-trip transmission timers used in hybrid automatic repeat request (HARQ) error-correction that supports reliable cell phone to base station communication.

There are many activities underway to overcome these penalties for adopting C-RAN, such as alternative architectural splits of the BBU/RRH interface. As with any major shift, the different architectural splits must be clearly defined and standardized, and it will be a few years before we see commercial implementations. During this transition period, CPRI and OBSAI remain the best bets.

Network functions virtualization (NFV) is poised to transform how mobile services are delivered. NFV lowers operational costs by eliminating truck roles for new service orders and automating service management. NFV decouples the functions from hardware, allowing operators to choose best-of-breed open hardware and software to best suit their business and customer needs. Investing in open software and lower cost hardware now can save money while eliminating vendor lock-in and enabling dynamic network innovation. The next step after NFV is mobile edge computing (MEC), which offers cloud-computing capabilities at the edge of the mobile network.

With NFV and MEC, operators can also reduce cost and optimize cell site densities by consolidating most if not all functions in one appliance, which should be open and able to support NFV and MEC. By consolidating switching, cell site gateway, NID and open server functionality into one box, operators reduce equipment footprint substantially. Value-added software appliances can also be added and spun-up as needed. Examples include mobile test facilities and VoLTE QoE monitoring.

Openness allows virtual network functions from many different vendors to operate simultaneously on an open platform, preserving this investment well into the future.

Boost Spectrum Utilization and Service Quality With LTE-Advanced

Mobile operators are now moving to the new LTE-A, which, when deployed with precision synchronization, reduces delay and enables coordinated transmission between base stations that improves cell edge performance and spectral efficiency of the network air interface.

With LTE-A, operators can increase spectrum efficiency while improving quality of experience for the end user.

Mobile operators want to ensure efficient use of their spectrum and improve performance at the cell edge. One way to do this is by using multiple-input and multiple-output, or MIMO. MIMO is a means for multiplying the capacity of a radio link using multiple transmit and receive antennas to exploit multipath propagation. MIMO techniques significantly improve performance, which is why most Wi-Fi routers are equipped with this technology.

Optimize Synchronization and Reduce Latency for High Performance

Another critical step is to ensure tight synchronization for clean handoffs, and to reduce transmission delays that negatively impact service delivery and quality of experience.

Cell towers and mobile networks can also benefit from coordinated transmission, which is why LTE-A requires base stations to communicate with each other via an interface known as the X2 channel.

In a backhaul environment, this channel traverses the backhaul network, often as far as the mobile core, and then is switched to the neighboring confederated base stations in order to facilitate coordinated multipoint (CoMP) transmission.

Latency of the X2 channel impacts the base station’s response time in adapting to changing signal/path characteristics. Reducing X2 latency has been shown by early adopters to significantly improve throughput and quality of experience at the cell edge.

C-RAN architectures that colocate BBUs lead to intrinsic latency reduction of the X2 channel. Although a facility in the central office is needed in order to switch the X2 traffic between BBUs.

Taking Steps Toward the Connected Everything World of 5G

In a white paper from Heavy Reading, Teresa Mastrangelo writes, “5G networks are anticipated to provide exponentially more capacity, lower latency, ubiquitous connectivity, as well as increased reliability and availability.”

She says “anticipated” because we don’t yet have specifications on what a 5G network will be. We do know what it must support: internet of things, visual/virtual assistance and full virtual reality, pervasive connectivity and unlimited mobility. Plus, incredible amounts of video.

More specifically, according to various sources, 5G is expected to:

• Reduce latency from 75-100 milliseconds to less than one millisecond
• Transport data 30 to 50 times faster
• Prioritize traffic so critical service jumps in front of non-critical service
• Use less power
• Allow end-to-end wireless transmission

Finally, 5G networks will be heterogeneous, supporting wired and wireless, physical and virtual, old and new, and multi-vendor components and devices.

The 5G Infrastructure Public Private Partnership (5G PPP) has been initiated by the European Union Commission to deliver solutions, architectures, technologies and standards for next generation networks of the future. It comprises industry manufacturers, telecommunications operators, service providers, SMEs and researchers that are focusing on increasing user data rates, and lowering latency for specific user types of applications. Many expect this effort to fuel the ongoing trend toward 1Gbit/s and 10Gbit/s (in shared infrastructure cases) backhaul rates, and reductions in latency across the network for specific classes of service.

As a member of the 5G PPP, ADVA Optical Networking is working to help establish standards and guidelines and co-authoring papers to provide insight to the group’s efforts. Similar organizations in the US and Asia are working on these issues as well.

According to reports from the 5G PPP, the following high-level targets for 5G performance are under discussion worldwide:

• 1,000X in mobile data volume per geographical area reaching a target of 0.75Tbit/s for a stadium
• 1,000X in number of connected devices reaching a density ≥ 1M terminals/km2
• 100X in user data rate reaching a peak terminal data rate ≥1Gbit/s for cloud applications inside offices
• 1/10X in energy consumption compared to 2010 while traffic is increasing dramatically at the same time
• 1/5X in end-to-end latency reaching delays ≤ 5ms
• 1/5X in network management OpEx
• 1/1,000X in service deployment time reaching a complete deployment in ≤ 90 minutes
• Guaranteed user data rate ≥ 50Mbit/s
• Capable of IoT terminals ≥ 1 trillion
• Service reliability ≥ 99.999% for specific mission critical services
• Mobility support at speed ≥ 500km/h for ground transportation
• Accuracy of outdoor terminal location ≤1m

Technology enablers expected for 5G include NFV and software-defined networking (SDN), in order to enable an elastic, cloud-like mobile network that can spin up new virtual functions and connect them to remote antennas as customer demand ebbs and flows. For this reason, centralized and cloud RAN facilities are foundational technologies for the 5G infrastructure.

For 5G, multiple research projects and standards bodies are investigating the architectural split of BBU/RRH that will enable the most efficient model comparing transport penalty versus NFV gain.

Considering the steps needed to build and deploy a 5G-capable network, it’s ever more likely that a high-speed, low-latency, protocol flexible infrastructure supporting centralized and cloud RAN will be required.

Does This Sound Familiar?

I don’t think it’s a coincidence that many of the solutions an operator can implement today to solve near-term challenges are also the right investments for 5G.

NFV, MEC, C-RAN, synchronization and coordinated transmission are enablers for 5G. The move to LTE-A will be accelerated once a C-RAN infrastructure is in place. By investing today in solutions like NFV, precision synchronization and consolidated appliances to tackle immediate challenges of OpEx reduction and cell-edge performance improvement, operators can lay the foundation for a 5G-capable network.