Andrew Costello, left, and Ron Phillips
Small cells are more than just an answer to persistent in-building penetration and high-density RF challenges. They are critical in satisfying user bandwidth capacity needs in difficult indoor environments like malls, stadiums and convention centers. These unique locations couple significant bandwidth demands with a largely stationary or nomadic user population. Strategic use of small cell sites allow network operators to focus available bandwidth in confined areas by adding improved service quality, but this opportunity comes with unique challenges.
Small cell deployment and installation challenges
Small cell deployments differ from macrocell deployments considerably. Because macrocells are relatively sparse and cover a three to five square mile area, significant amounts of time and money are spent in preparing the site, including for backhaul, power and antenna optimization. While a new macrocell in the US can easily cost more than $250K, IBB Consulting has found small cell costs to be less than 10 percent of macrocells. Support infrastructure like site access, power/transport and security comprise the majority of those costs.
While operators can build the infrastructure from the ground up, it can be very expensive, with challenges typically found in two key areas: providing backhaul to the venue and distributing the backhaul within the venue.
Options for providing backhaul to the venue include getting a dedicated or best-effort Ethernet circuit to the venue from the local ILEC, CLEC or cable operator. Wireless point-to-multipoint providers using the LMDS band can also provide this solution using a rooftop or external antenna in the venue. Backhaul selections should include any forecasted consumption changes and any necessary redundancy.
When distributing to the backhaul within the venue, the ability to leverage any existing Ethernet wiring at the venue may appear attractive because of CAPEX savings. However, problematic wiring can quickly nullify any cost savings due to outages and maintenance. If the infrastructure can support Power over Ethernet (PoE), this will simultaneously address the power supply issue, but the distance limitation of Ethernet can increase costs by requiring additional PoE switches. When small cells are powered from a centralized, intelligent source (PoE switch) instead of individual sockets, it provides two additional advantages: power source diversity, such as battery backup, and the ability to power cycle the device remotely.
When outfitting aesthetically-demanding sites or locations like solid concrete structures where internal Ethernet wiring is challenging, a mesh backhaul over Wi-Fi helps solve logistical issues. Mesh backhaul does not address power supply challenges and is less reliable, but it has the benefit of being cheap, quick and easy to deploy when compared to drilling conduit and snaking cable. With emerging Wi-Fi technologies of 802.11ac maximizing the 5GHz band, MIMO, and 256-QAM, the bandwidth performance of Wi-Fi in indoor multipath environments has improved significantly.
Naturally, significant coordination and support are required from the venue owner in deploying small cells. A venue owner may desire a carrier-agnostic solution, so that all patrons can benefit from the installation. Because small cell networks are strongly tied to the carrier, collocating Wi-Fi access points (AP) can help create ubiquitous access. Most major small cell and Wi-Fi AP vendors plan to offer combined small cell and Wi-Fi access points with various levels of integration.
Another installation challenge is securing both the physical small cell unit and corresponding backhaul links. Small cells are a critical part of the operator network and tie directly into the mobile network core. This typically happens over an untrusted backhaul link, such as an existing venue network or third-party backhaul vendor. The small cell unit and backhaul circuit are usually within the public's physical reach and can be easily compromised, opening an operator to spoofing, man-in-middle and denial of service attacks. Coupling 3GPP Certificate Enrollment with digital certificates and a Public Key Infrastructure (PKI) enables mutual authentication of the small cell and operator network at small cell boot. The mobile core network can periodically reauthenticate the small cell to ensure it has maintained its connection and has not been tampered with via a remote attack.
Optimization is no small matter
After completing installation, the next important step is optimizing the radio network for the small cells. An extensive amount of testing and radio planning, in addition to optimization, is conducted for each macrocell. But this is not cost-effective for low-cost small cell deployments. Operators currently use approaches that reserve dedicated frequency allocations for small cells and coordinate the small cell frequency with that of the serving macro cell. As Self Optimizing Networks (SoN) becomes more common, many small cell optimization tasks can be automated using this approach.
Device manufacturers have also begun introducing features that allow for efficient network management. For example, most operators now require Wi-Fi offload capabilities on the device that encourage or force the user to pass traffic across available Wi-Fi networks. As new capabilities like ANDSF and Hotspot 2.0 become prevalent on mobile devices, users will have increased capability to spread traffic across multiple air interfaces based on availability and activity.
Rethinking ongoing maintenance
Day-to-day maintenance of the small cell also requires a different approach, since site access typically requires coordination with the venue manager. For large sites, the venue's technicians can possibly be trained to perform basic maintenance tasks. Remote provisioning and updates will be important for managing the network maintenance costs.
There are many considerations when planning an indoor small cell deployment from site access, power/transport, and security, but the time and effort is justified when a well-planned and executed small cell site keeps customers connected, happy and coming back.
Andrew Costello ([email protected]) and Ron Phillips ([email protected]) are principals with IBB Consulting, advising mobile operators, venues and Wi-Fi service providers on wireless network deployment and optimization strategies.