High Power Distributed Antenna System (DAS) Introduction
With the explosion in wireless data services and smartphones popularity, people need instantaneous communication at anytime, anywhere. Mobile service providers need increase capacity and extend coverage range which has been traditionally accomplished by adding new macro cell towers. However, existed BTS and repeater station address has been more congested, to find a new macro cell site is very difficult. The distributed antenna system (DAS) can provide a flexible solution to extend coverage and capacity, as well as provide several mobile service in one device centrally.
The mobile operators generally install their coverage equipment at the place where they selected separately, need many kinds of different equipments and many precious station address. It is serious resource waste in fact. The DAS is a multi-band coverage system which could provide multi-frequency and multi-mode mobile coverage service in one device, supports network sharing. A 3-band DAS such as integrated CDMA, GSM, UMTS service could be installed by builder then lease the equipment to 3 operators separately. To operators, they reduced facility expenses and maintenance cost by sharing single facility in a single location, both CAPEX and OPEX are saved.
The DAS is a highly flexible system which could carry RF signal from original source to anywhere placed remote nodes close to the user. The DAS added carrier capacity, reduced multi network investment and maintenance budget, got rid of limited or strict installation space and policy. The DAS must will lead the mobile coverage trend in future.
The DAS can provide all of 2G,3G, 4G and some private network wireless services. The specific frequency band is shown as below. All kinds of service can be combined into one DAS expediently according to custom demands.
2G: 900M GSM, 800/900M SMR, 1800DCS, 1900M PCS
3G: 800M CDMA, 2100M UMTS
4G: 2.4-2.6G LTE
The DAS suit many scenes such as follows:
The metro is a full closed traffic system at where the facility installation and maintenance is highly limited. The operators are forced to provide all kinds of mobile service in very limited space, so the DAS may be the best solution to it because of its high flexibility and high integration level. In a metro DAS, all the RF resources (2G, 3G, 4G) could be centralized together first, then distributed over long distances via fiber to distant radio heads which are mounted along railway flexibly. Because of the flexibility of fiber, the capacity can be delivered to different areas depending on the network need. Integrating several service into one facility simplifies the maintenance difficulty of whole system, it is very important to the metro of strict management. The DAS can be placed inside the corner and utility poles or wall bracket-mounted, its flexible installation is very valuable to metro too.
2. Tunnels, Canyons, and Coastal Areas
The physical features of tunnels and canyons shield the RF signal from traditional macro cell towers naturally and its region is irregular which it is hard to cover. The high power remote heads of DAS can be cascaded via fiber to form a network where antennas can be placed arbitrarily along with its topography. The DAS can deform its coverage region arbitrarily, so it is very suitable for these irregular areas. In these areas, nature factors are harsh such as rain, dirt, dust, high and low temperature and sea-salt corrosion. The DAS is a full sealed system which is insulated from external and suitable for all-weather using.
3. High-End Suburban, Nature Preserves And Historic Communities
The traditional macro tower will look out of tune with ambient environment, and high RF power in single point will affect resident mental too. People will unconsciously think about radiation problem after all. The DAS can distributed RF power at single point to several low power remote heads which have reduced RF radiation finally. The DAS facility can be designed to be compact which even to be placed into street lamp pole. Because the fiber is very tiny, the remote head of DAS can be designed to be invisible. The DAS solution could be highly harmonious with environment. Attaches to existing utilities, like streetlights or overhead utility poles, are aesthetically pleasing and do not require new zoning. This is particularly appealing to suburban communities happy to gain coverage nearly invisibly.
4. Campus Solutions
Mobile operators have to often take care thousands of students who need massive data service of indoor and outdoor in university campuses. A great quantity of rooms and large open region need indoor network and outdoor network must be bridged. A cascaded DAS system can build a seamless network and coverage indoor and outdoor region at the same time.
5. Stadiums And Large Venues
The stadiums and large venue are typical hotspot where need jillion data and calls service and its need change greatly over time. Traditional macro cells couldn¨t optimize the dynamic services in real time. In the case of the DAS, the centralized resources are signal sources from a base station hotel. This architecture provides a lot of flexibility for mobile operators to optimize the capacity in their networks while serving subscribers when and where they need that capacity.
In summary, the DAS has several advantages as below:
1. Distributes RF capacity from centralized radio suites to strategically placed remote nodes close to the user, and cascade remote nodes built a network which could change coverage region flexibly.
2. Integrate multi-band and multi-mode service into one device, easy to install and easy to maintain. Site selection is not a difficult problem anymore. Save both CAPEX and OPEX.
3. Suitable for both indoor and outdoor coverage. Make improve capacity and coverage design easier.
4. Changed business model, make it is true that integrator can built coverage system first then lease it to carrier operator, mediated site selection and operation conflict of operators farthest. So that gets the best cost performance.
The DAS is composed of host unit, remote unit and network monitoring & management unit in general.
The host unit is small-signal part of the DAS, communicating with the base station and network management system. A host unit is located near a base station even into a base station. On the forward link, the host unit receives RF signals from the BTS and digitizes them and then transform them into optical signal which will be transported over fiber to the remote units. On the reverse link, the host unit receives the optical signals from the remote unit and converts them back to RF for the BTS.
There is a network management system board in the host unit. This system collect all the alarm and monitoring information of both host unit and remote unit, and then exchange these data with BTS. The management system could accomplish all facility parameters configuration and transfer. It is the brain of the whole of DAS.
The remote unit is big-power part of the DAS, receives the optical signal from host units and transform them into RF signal and then transfer them to antenna after amplifying them. The heart of the remote unit is several MCPAs (multi carrier power amplifier) which amplify the signal to about 50W separately, each MCPA amplify only one kind of signal. Typical mounting options for the remote unit including pole-mount, inside pole-mount, wall-mount, and sub-terrain vault-mount.
The remote unit is fully sealed and meet IP-65. It is designed to be long and thin cuboid and cabinet mechanical structure in general. The cuboid remote units could be highly harmonious with environment, the cabinet ones have more flexible and more easier to be mounted.
On the forward link, the Remote Unit receives the optical signal from the host unit and converts it into RF to be distributed via an externally mounted antenna. On the reverse link, the remote unit receives the RF signal from mobile phones and then transform them into optical signal and transports it over fiber to the host unit.
Network monitoring & management unit
The mobile operators need know well the operation status of the DAS in real time. A high efficient network management system is necessary. The management system could accomplish system configuration, alarm, parameter setting, download software, read running status etc. Troubleshooting will be more easier through this management system. Engineering technical personnel can access the DAS with a notebook computer via a piece of network cable on site. Both the host unit and the remote are all accessed in general.
A typical tri-band Distributed Antenna System specification is shown as below:
Tri-band Distributed Antenna System
Full operation bandwidth system supports multi-mode applications.
l Supports both Indoor and outdoor DAS applications while meeting the need of Coverage and capacity expansion.
l Supports all major modulations in mixed mode with highly efficiency and linear MCPA up to 40W per frequency band.
l One MU supports up to eight RUs.
l Comply with 3GPP, 4G & FCC
l Remote control with OMT software over LAN
l Output power control by software.
l Optical link auto gain control.
l Fully sealed RU, maintenance free electronics for harsh outdoor applications
l Optional Passive unit for duplexer input.
The Tri-band Distributed Antenna System provides an effective solution for coverage enhancement. It is suitable for applications where large signal coverage is required, such as citywide enhancement, highway and canyons, campus, underground tunnels, airports and convention centers, etc.
The system consists of Master Unit (MU) and Remote Unit (RU). The MU¨s modular design can support up to eight RUs by adding optical module. The RU¨s fully weatherized enclosure with built-in AC power surge protector. The RRU is designed for installation at any outdoor environment. Product reliability and lower maintenance cost is achieved by advanced design.
Functional Block Diagram
Operation and Maintenance
Provide OMT software via Ethernet connection for the commissioning of DAS system.
l The MU and RU are communicated over the optical Fiber, hence, the RUs can be remotely controlled by connection to MU locally or remotely
l Adjustable parameters include: On/off Switch, Uplink Gain Setting, Downlink Gain Setting, Alarm Threshold Setting, etc.
l Monitored parameters include: Downlink Output Power, Temperature, Optical Power, etc.
l Alarm parameters include: Power Supply, Optical Alarm, Door Open, Temperature, Software, Hardware, shutdown, etc.
l Provide the optional OMC system to monitor a large volume of DAS system remotely