Month: September 2016
Another of the enduring challenges in matching up a DAS with a mobile base station has been the need to use RF as the method of interface, which adds complexity and cost to the deployment. But to date, DAS equipment has not been able to use the Common Public Radio Interface (CPRI), which has been defined for base stations. Now, DAS equipment that does use CPRI is emerging, solving several key problems.
CPRI defines the publicly available specification for the key internal interface of radio basestations between the radio equipment control (REC or basestation) and the radio equipment (RE, or radio head). The companies cooperating to define the CPRI specification now include Ericsson, Huawei, NEC, Nokia Siemens Networks, and Alcatel-Lucent. The CPRI specification has gone through several revisions, and today it is at version 5.0.
The idea behind CPRI was to create an open standard for interfacing basestations with radio heads. But in reality, CPRI is neither common nor public, as it is not truly an open standard. Instead, similar to what happened with the Integrated Services Digital Network (ISDN) for public branch exchanges (PBXs), each manufacturer developed its own flavor of CPRI that works only when interfacing its own basestations with its own radio heads.
The DAS head-end interfaces with base stations through the RF signal. This has been true since the inception of DAS more than 20 years ago. However, there is a significant power mismatch between base stations and DAS head-ends that must be accommodated for this interface to work. A typical base station puts out about 40 W, and a DAS head-end takes in roughly 0.25 W. Feeding 40 W into a DAS will destroy the head-end. As a result, the base station’s power must be severely reduced before it can interface with the DAS.
There are several challenges with reducing base station power output:
• Complexity: Base station power is reduced with racks of passive equipment called attenuators. All of this external “plumbing” between the base station and the DAS adds to the size, complexity, and cost of the deployment.
• Space: Racks of attenuators take up floor space, making a DAS deployment much larger than it needs to be. In many cases, there may not be enough floor space at the intended facility to accommodate the entire deployment, so a separate, off-site facility must be built. This added expense can be a deal-killer for many mobile operators.
• Heat: RF attenuators generate a lot of heat, making it necessary to spend more on air conditioning in DAS deployment areas.
• Cost: The need for attenuators and the need to invest manpower resources in designing and deploying all this RF plumbing adds capital and operating expenditures to the overall deployment, worsening the DAS business case for mobile operators.
• Inefficiency: Mobile operators invest in large, hot, power-hungry amplifiers for their base stations, only to have their power substantially reduced in the actual deployment. Amplifiers are one of the biggest cost drivers in a base station.
DAS installations are pretty expensive. Hence to justify this investment, providers and carriers prefer long contract terms, with ten years quickly becoming the industry standard. In a carrier-owned DAS, a wireless service provider pays for the equipment and installation costs, as well as maintenance and upgrades. In return, the service is typically exclusive to the carrier that installed the DAS. When a third-party neutral-host provider installs a DAS, this entity bears all of the costs, which can be recouped by charging any or all of the service providers to have access to the system.
Within the United States, Corning Mobile Access, CommScope, and TE Connectivity all serve as DAS hardware vendors. Other manufacturers include Axell Wireless, Comba, Ericsson, Kathrein-Werke, NSN, Optiway, PowerWave Technologies, Solid, and Zinwave. In the world of cellular service providers, AT&T has a large and growing, albeit not exclusive DAS practice.
CommScope offers outdoor wireless solutions, such as the Andrew DAS, which supports all current system architecture and power ranges and is ready to handle more advanced technologies like high-speed packet access (HSPA+) and evolution-data optimized (EV-DO).
FlexWave Prism manufactured by TE is also designed for outdoor use. The package offers mobile operators a way to extend macro network coverage for 2G, 3G, and 4G services. TE’s indoor product is called the FlexWave Spectrum, which can extend wireless services throughout a building, multiple buildings, or a campus.
TE also has a product geared specifically toward enhancing public safety. The appropriately titled TE Public Safety DAS provides distortion-free transmission and distribution of information. It has been used worldwide to improve vital communications in systems for first responders, government, transit, commercial enterprises, education, security personnel, and the military. It functions both indoors and out.
Corning MobileAccess DAS solutions include the single operator MobileAccess 1000 and the multi-operator MobileAccess 2000. Both are designed for indoor use and have a single, broadband infrastructure with service-specific, chassis-based modules that automatically groom wireless signals. The 1000 model hosts up to four wireless services in medium-to-large-scale environments; whereas, the 2000 model’s modularity enables users to introduce new wireless or operator services at any time and is suitable for large-scale, multi-operator facilities.
Like Corning, SOLiD has two flagship DAS products that differ mostly by scale and capacity. The cost-effective EXPRESS single-carrier DAS provides in-building or outdoor wireless service for a single wireless provider across multiple frequency bands. It typically uses just one fiber to connect a building. The alliance DAS system seems to be much of the same, designed as a multi-carrier solution, and presumably a less cost-effective one at that.
The manufacturers listed so far sell complete Distributed Antenna Systems, Oberon Wireless seems to distinguish itself by selling system components. Its WiFi and DAS antennas come in indoor/outdoor varieties, with a variety of frequency bands to choose from. Some models are dual band, coming in either puck or dome styles. This company also sells the mounting brackets required for installation.