lightRadio, a new wireless networking paradigm, brings service providers innovations that improve capacity, coverage and performance just when they are needed most.
Innovating to address service provider challenges
To meet the skyrocketing demand for bandwidth, wireless service providers face a number of challenges that make today’s networks economically unsustainable including:
- Adding more towers, antennas, radios and processing capacity
- Supporting new technologies
- Increasing spectral bandwidth
- Making better use of cell site capacity
Based on Alcatel-Lucent Bell Labs innovations, lightRadio is designed to optimize total network costs over time and to make the most of each wireless service provider’s existing assets and capabilities. Figure 1 illustrates the lightRadio architecture, including:
- The main components: Antennas, radios, baseband units, controllers and management
- Two different wireless scale points: Conventional macro cells and smaller metro cells
- Three different baseband processing configurations: At the base of the tower (conventional baseband units), in the radio head (all-in-one) and centralized, pooled baseband processing (in the cloud)
Making antennas smaller, smarter, stronger
Antennas have a significant impact on consistency of coverage and capacity. Historically, service providers added passive transmit and receive antennas for each radio and technology when they needed to improve these aspects. With lightRadio antennas, this is no longer necessary. lightRadio uses smart active antenna arrays (AAAs) that deliver multiple-input multiple-output (MIMO) gains and sophisticated beamforming in a very small footprint. With these capabilities, radio frequency (RF) energy can be dynamically directed exactly where it is needed based on changes in cell loading and traffic density. Figure 2 illustrates one of the innovative AAA designs used in lightRadio.
The lightRadio AAAs can:
- Improve capacity up to 30 percent with vertical beamforming
- Lower power consumption by improving coverage
- Improve antenna robustness by allowing the array to be reconfigured to reduce the impact of individual element failures
The lightRadio architecture also supports conventional passive antennas. Together with centralized baseband processing, these antenna solutions support advanced inter-cell interference coordination (ICIC) schemes between neighboring cells. This significantly improves signal-to-noise ratios.
Making radios multi-band, multi-purpose
Deploying capacity in new spectral bands usually means buying expensive new spectrum and equipment. If the new band is lower in frequency than existing bands, coverage will improve because lower frequency bands have better propagation and cell reach. If the new band is higher in frequency, its reach will be more limited. This can create coverage holes between base stations, particularly when cell sites were chosen based on a lower frequency spectral band. Coverage holes can decrease quality of experience (QoE) and are expensive to fill. lightRadio uses radios that can operate across multiple spectral bands. Service providers no longer have to deploy new radios to support new bands. These new radios can also be incorporated into a smaller number of lightRadio remote radio head (RRHs) to support ongoing capacity increases. As a result, “light radios” dramatically reduce capital expenditures in multi-band deployments. They also help service providers deal with tower loading issues. Today, the size, weight, wind loading, visual appearance and leasing costs of cell towers have become blocking issues for the evolution of radio networks. At most cell sites, radios are on the tower in an RRH configuration. Macro cell sites are typically divided into three sectors with a separate RRH required for each frequency band. Because some service providers have sites with five different frequency bands in three sectors, 15 RRHs on a cell tower is not uncommon. To make matters worse, multiple service providers often share a tower that is leased from a third-party provider. New antenna configurations, such as 4 x 4 MIMO (four transmit antennas and four receive antennas) further increase complexity. As illustrated on the right side of Figure 3, lightRadio significantly reduces this problem. Although a tower is illustrated here, these problems are most acute for dense urban areas where the RF equipment is more typically mounted on the top or side of a high-rise building or on a mast.
Making baseband processing more efficient, effective, economical
As wireless service providers look to increase capacity and improve network economics, they may deploy Long Term Evolution (LTE) in a new frequency band, such as 700 MHz or 2.6 GHz, in a new antenna configuration such as 4 x 4 MIMO. They may also take advantage of new technologies such as LTE-Advanced. LTE-Advanced provides carrier aggregation — “bonding” together separate frequency bands — and sophisticated methods for coordinating multiple base stations. These methods include coordinated multipoint transmission (CoMP) and dynamic ICIC. CoMP increases spectral efficiency and improves end-user performance. When engineered to take advantage of centralized baseband processing, CoMP and ICIC technologies can significantly increase network efficiency. lightRadio supports both current and anticipated wireless technologies. In a lightRadio architecture, the baseband module (whether centralized or remote) can be dynamically reprogrammed to support multiple combinations of Wideband Code Division Multiple Access (W-CDMA) and LTE technologies and their evolution. That means a wireless service provider could start with a baseband unit that is fully W-CDMA and gradually reconfigure its software as needs change until the same hardware is fully used for LTE. Remote software configuration reduces time and costs as service providers evolve to support new technologies. lightRadio also allows wireless service providers to seamlessly migrate baseband processing from a remote site to a centralized baseband processing pool. Digital modules from the remote baseband unit can be redeployed in the centralized processing site. Alternatively, they can be configured to operate as a coordinated pool of resources at the remote site. lightRadio supports two baseband processing options with different backhaul requirements:
- Processing baseband signals on the remote cell site in a baseband unit (BBU) at the base of the cell tower or integrated with the radio head (all-in-one BTS). This option requires backhauling of asymmetric, latency-insensitive, relatively low bit-rate streams of native IP traffic. We call this method “IP backhaul.” IP backhaul transport is supported over copper, microwave and fiber infrastructures.
- Processing baseband signals in a central location as part of a pool of resources “in the cloud.” This option requires backhauling of radio signal samples which are symmetric, latency sensitive and typically high bit rate. We call this method “CPRI interconnect,” referring to the Common Public Radio Interface (CPRI) specification typically used to transport these signals.
- CPRI interconnect requires point-to-point fiber links or a wavelength division multiplexing (WDM) passive optical network (PON) with 10 Gb/s per wavelength. However, it also benefits from Bell Labs’ compressed I/Q transport. Used with LTE, the compressed I/Q algorithms reduce bandwidth requirements by a factor of 3 compared to uncompressed I/Q transmission.
This architectural flexibility allows the widest deployment and reuse of existing infrastructure, using a combination of IP backhauling and CPRI interconnect. It also helps to reduce total cost of ownership (TCO) and accelerates deployments.
Increasing capacity usually means increasing the number of carriers (the W-CDMA method) or improving the spectral bandwidth for each carrier (the LTE method). If spectral increases are in the same band, the same equipment and radio technology can often be reused. If spectral increases are in a new frequency band, new antennas, radio and baseband equipment are required. Because capacity needs to match multiple factors — demand, device populations and related usage intensity — service providers typically need a combination of existing and emerging technologies. lightRadio lets service providers effectively deploy a solution that matches user demand and is optimized from the antenna to the baseband processing and controller elements. In a lightRadio architecture, baseband digital processing modules are built with new System on a Chip (SoC) technology. The SoC technology:
- Incorporates previously discrete, technology-specific components into a single device that offers high performance at low costs and is technology-agnostic.
- Can be remotely reprogrammed to support new features and even new radio technologies. This means that when W-CDMA customers shift to new LTE-based devices, the baseband module that has been serving them can be remotely reprogrammed as an LTE baseband module.
When capacity expansions are in new spectral bands, it may mean service providers have to acquire spectrum that covers a much broader area than the locations where demand has peaked. For example, a dense urban site might need four carriers or more for W-CDMA. But this is probably much more than a rural location need. In contrast, increasing a cell site’s density lets wireless service providers use existing spectrum assets to increase the effective serving capacity. This is the key reason for deploying smaller macro cells and metro cells, sometimes called “pico cells.” lightRadio supports two approaches for macro cells:
- Putting all baseband processing into a single multi-technology base station
- Transporting baseband radio signals to a centralized location that houses the baseband processing equipment
These approaches are complementary. The choice depends on availability of backhaul bandwidth, elasticity of demand patterns and operational costs. Outside of urban areas, backhauling CPRI signals to a central location may not be cost effective. In these cases, a more traditional BBU is a better fit and cell sites are often served by microwave. Considering the size of wireless networks and the number of infrastructure configurations, no service provider wants to change the available features when a user moves between cells or locations. Nor do they want to invest in network assets that have a limited effective lifetime. To help service providers address this challenge, the lightRadio product family uses common digital baseband components across different products and radio technologies. This gives service providers consistent functionality and reusable common hardware and software components. Deploying smaller cells, or “metro cells,” at cost-effective locations offers another way to increase cell site density. Metro cells do not typically provide contiguous coverage. Instead, they augment a macro network in “hot spots” that have high traffic density. In the lightRadio paradigm, metro cells are built on the same SoC technology as the macro cells and use the same backhaul resources. Anticipating the need for coherent metro cell and macro cell optimization, Alcatel-Lucent extends the concept of self-optimizing networks (SONs). A new layer of understanding, called “wireless IP intelligence,” helps service providers respond to rapidly changing demand patterns. It optimizes the entire network, including the RAN, packet core and both licensed and unlicensed spectrum assets such as Wi-Fi® access points.
Stay tuned: lightRadio technical details to follow
This technology overview offers just a glimpse into how lightRadio addresses service provider challenges. Watch for additional articles that take a closer look at the benefits of key technical advances, such as the wideband active antenna array architecture. We’ll explore the factors that make these antennas the ideal evolution of low footprint RF hardware for base stations and a major step forward in beam-shaping flexibility. To contact the authors or request additional information, please send an e-mail to firstname.lastname@example.org.