Metrocell backhaul ripe for revolution

In the space of a few years, last mile backhaul equipment has quickly evolved from a mere base station component to a key element that must be carefully and independently chosen, impacting the quality of service for the customer.
But as “wireless backhaul” increasingly harnesses several different technologies, mobile operators must manage many different types of backhaul equipment, increasing the challenges for maintenance and repair. And out of all the base station form factors, metrocell backhaul is the one posing the greatest challenge for operators, since practically all backhaul types are applicable to these small public access cells.
This has led some firms to tout the concept of a “transformer,” a single unit which can act as different types of backhaul connection to increase flexibility.
Given the large number of metrocells which will be deployed, compared with base station volumes in the existing macrocell world, the mobile industry will have to take advantage of low-cost consumer electronics radios and adapt them to carrier grade applications, in order for small cells to be economically viable.
Metrocell backhaul equipment is going through the same evolution, whether integrated with the metrocell radio or manufactured as a separate unit. Such cost optimization implies it will not be practical to repair metrocell equipment onsite, but instead malfunctioning devices will have to be replaced with spares and taken back to lab.
In order to minimize service degradation, mobile carriers will have to ensure efficient stock management and quick physical installation. Self-organizing networks (SON) and remote configuration will do the rest of the work.
As always in technology, there is no single winning solution for metrocell backhaul, since the main alternatives available - namely point-to-point or point-to-multipoint microwave, NLOS and millimeter wave – all have their pros and cons. This is why the industry is reaching the consensus that there will not be a definitive metrocell backhaul solution, but a bunch of alternatives that will be combined depending on the particular conditions of each deployment.
But, would it be possible to have a single backhaul device capable of “transforming” into any of those alternatives?
Following the latest developments in the industry, the answer to the question seems to be ‘yes’. This has resulted from several stages of evolution. The first evidence of backhaul convergence was the appearance of baseband system-on-chip (SoC) solutions supporting traditional microwave and NLOS (OFDM) modes of operation. DesignArt, which was recently acquired by Qualcomm, was almost two years ago the first silicon vendor to release such a solution to the market.
Other silicon giants are taking similar strategic positions. FPGA vendor Xilinx has been the latest to follow this trend, now owning NLOS and microwave IPs developed by Estonian modem solutions provider Modesat Communications. Broadcom, which separately acquired OFDM specialist Beceem and traditional microwave silicon vendor Provigent, has not shown any evidence of plans for a merged backhaul SoC yet, but given its various assets, this is very foreseeable.
If PmP capabilities are not implemented in the SoC itself, they can be supported in a separate processor. All this means “backhaul transformers” may not be just science fiction.
There are obstacles though. Perhaps the most challenging part of such a device would be the radio, since the frequency bands that need to be covered span typically from 2.3-GHz to 60-GHz.
There is currently no software defined radio (SDR) in the market capable of supporting such a wide spectrum band, though in our opinion, a modular design with several radio add-on options could be an alternative, especially considering the high cost increment that a sophisticated SDR radio would add to a price-constrained metrocell.
Also, considering the need to switch antennas depending on the frequency band and topology (PtP or PmP), the resulting solution could also be too cumbersome. Industry initiatives to standardize baseband radio and radio antenna interfaces would be the perfect solution to that and are urgently required to turn the transformer into a commercially viable option.
However, the potential to revolutionize the metrocell backhaul sector and address many of its challenges is clear. California-based FastBack Networks is the first vendor publicly to have announced its intention to develop backhaul transformers. Although still in their infancy, disruptive proposals such as backhaul transformers are what operators need to give the final push to the metrocell revolution.
This analysis was contributed by Esteban Monturus, principal analyst and backhaul specialist at Maravedis-Rethink.