A revolution in network coverage optimisation will eliminate costly excess infrastructure, claims Joe Moore, managing director of Sigma Wireless.
Optimisation experts estimate that most Mobile Network Operators currently install as much as 30% more infrastructure than is required to achieve acceptable service levels than would be the case if the optimisation process was completed fully. The process is complex and very costly, not least because of the difficulty in getting access to transmitter sites, shutting down the network and carrying out changes at the top of the mast. However, the added difficulty for many is how to optimise a 3G network at the initial phase and then as the network matures.
The fundamentals of the problem
The fundamentals that force Mobile Network Operators to install excess infrastructure begin almost from the moment the decision is made to roll out a new network. Once that decision is made, the key challenge is to do so in an effective and speedy fashion. Pressure is on to find new sites, obtain planning approval, install and commission the radio and ancillary equipment — in as many selected sites as possible, in a short timeframe.
Sites are considered commissioned if measured results correspond to design predictions. When results fail to correspond to design, then some diagnostic work is carried out to assess if the drive test results are more accurate or if the site equipment has some failure mode. Each time this work is carried out, the operator must plan to get access to the site. This can involve getting the landlord’s permission if the site is not owned, shutting down the transmitter site, and either adjustment of the tilt angle of the antenna or even replacement. At some point in the optimisation process, priority shifts to commissioning new sites at the expense of actually achieving full optimisation. The effect is non-optimal QoS and extra cost.
In addition to the logistics and project management issues outlined above, there are new technical problems associated with 3G network rollout that suggest a new approach is required. The following statement appears in the 3GPP technical Report TR 25.802, which summarises the need for the ability to tilt antennas remotely (in effect making remote variable tilt a de facto requirement!).
“Because of the interference limitation property of the CDMA-based [Code Division Multiple Access] UTRAN [Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network], the tilting of antennas is essential for the successful operation and optimisation of UMTS network coverage. It would be very beneficial if it were possible to remotely control the tilting of antennas in order to optimise radio coverage areas.
The ability for the operator to control the electrical tilt of the antennas remotely from the O&M [Operations & Maintenance] Network is currently possible via the implementation-specific interfaces between Base Station (Node B) Element Manager and Base Station. A “remote control” mechanism decreases the costs incurred by the operator for site visits to change the tilt of the antennas manually and simplify the redeployment of antennas in a large network.”
Experience to date suggests that clusters of sites need to be adjusted between 3 to 7 times before final settings. Ensuring good signal to noise ratio for 3G site clusters is a complex task. If for some reason, the adjacent site’s coverage is not as predicted, one possible corrective measure could be to adjust the antenna pattern of a particular site. Once this ‘corrective’ measure has been taken, each adjacent site should have its performance re-tested to check for adverse effects.
Being able to adjust a cluster of cells sites simultaneously speeds up the process and avoids a sequential approach to optimising.
The solution to this problem is to make the optimisation process so easy that there is no need to compromise the final stages of optimisation and ensure that the ongoing optimisation requirement is routine and inexpensive, according to Joe Moore, Managing Director of Sigma Wireless Technologies and one of the pioneers of the latest technology solutions — integrated Variable Electrical Tilt (iVET) antenna technology.
Network Operators are currently deploying Variable Electrical Tilt antennas to enable them to make adjustments to the tilt angle locally, either manually or by using handheld programmers or laptops. Acceptance of this technology is accelerating and operators are moving quickly to the next stage, Remote Tilt Adjustment.
The key enablers for the adoption of this technology are the availability of new antennas that facilitate ‘open-standard’ as well as the existing ‘vendor-specific’ communication protocols in the same product and the availability of both Wireless and Wide Area Network (WAN) Ethernet communication conduits, at an affordable price. These options allow Network Operators a variety of adoption strategies and control approaches. Some antenna management systems now being made available include an independent wireless option, such as the Sigma Wireless Blustream System (wireless over IP) plus an OEM integrated solution whereby management is controlled over the Operation and Maintenance system provided by their OEM suppliers.
Making remote tilt adjustment possible
Remote tilt control, requires two new enablers:
* New Antenna technology
* New Antenna Management Systems (AMS)
New antenna technology
Operators need to know that antennas deployed in the field are both future-proofed against changes to control software and, where a mixture of infrastructure vendors are used, that the antennas are flexible enough to work on all major control protocols. Sigma Wireless has just launched its new Multi-Protocol AQUA antenna range which is capable of operating on multiple protocols such as the AISG, Ericsson and the upcoming 3GPP standards. This latest innovation offers more options to operators and is a further enabler of the remote management of antenna line devices and playing a part in simplifying the optimisation process.
Additional to the control protocol used to make the adjustment in tilt angle, the matter of whether to follow a migration strategy from manual electrical tilt (MET) to remote electrical tilt (RET) is of key importance. The latest approach is to ensure that the antennas deployed are ‘RET capable’ from the start, instead of following the more expensive migration strategy (MET upgrade to RET) approach.
Sigma Wireless has adopted the ‘RET capable’ approach with the Tilt Controller integrated inside the antenna housing and has developed its patented integrated Variable Electrical Tilt (iVET) for superior performance and reliability. This unique approach delivers the following cost and performance benefits; lower visual impact, smaller size, elimination of field installation errors, positive adjustment controls through its closed feedback loop system. This technology is now mature and is being rolled out in earnest. Additional benefits appear at the installation programming stage, because the iVET antenna has a single identity — with all software parameters programmed in the factory making it very simple to install. As an extension of its integration strategy, Sigma Wireless has also moved on to integrating ‘third party’ amplifiers with the same benefits as described above.
The key technical design features of this product family are:
* High levels of pattern control through the tilt range.
* Patented iVET which ensures complete control of the pattern tilt without generating potential IMP sources.
* Capability to be remotely controlled over dedicated Antenna Management System or the O&M system provided by major OEM network suppliers.
Antenna management system descriptions
Antenna Management Systems (AMS) can either be an integral part of the operation and maintenance facility or can be a standalone sub-system. Both solutions have the following core elements:
* central database
* communication link to the Node B site
* interface to the antenna line devices (antenna and amplifier).
The decision to take a particular approach may be driven by cost, operational integration or even security aspects.
The central database is the repository of all site specific, antenna line information holding details such as serial numbers, manufacturer, technical specification and tilt/gain adjustment ranges. The central database is connected to a communication server, which manages the interrogation of site devices or the site control unit. Changes can be made from this control point which also receives updates of changes made in the field. A record of all changes is kept on the database.
The connection from the central database, stand-alone or integrated, can be set up over the internet using a wireless connection or over the Ethernet network of the Wide Area Network already in place to communicate with all radio equipment. Each site can be assigned an available internal IP address and, with this, each device is allocated a sub-address. In the case of the wireless option, each site is issued with a dynamic IP address using a standard GPRS SIM card. Security aspects of both options are to be managed within the existing IT security procedures of the Operator.
Sigma Wireless has developed a communication platform which is based upon the AISG standard and is capable of operating over Internet Protocol. The platform was taken because of its ubiquity and the prevalence of all types of standard communication tools using this technology. This approach also simplifies and makes the equipment required to manage antennas much more affordable than proprietary based software platforms. The Blustream antenna management system offers a wide variety of control options to operators and can either be integral to the OMC system or standalone from it if required.
This mode of addressing the site devices is suitable when the antenna and RET unit are fully integrated as a single device. In this instance the iVET has its communication and operational parameters pre-programmed inside the antenna, during manufacture. With this, the communications link from the central database is direct to the required device, without the need for intermediary processing capability and thereby reducing cost. In this scenario the site equipment is simply a communication conduit — “plug and play” either using a GPRS modem and/or the existing Ethernet connection.
This solution facilitates a very simple installation process. All of the antenna parameters — including tilt range — are set during manufacture, leaving only site specific information such as site name, sector and orientation to be programmed at site. This reduces the degree of on-site interaction required and actual installation time. Once the antenna is connected to the communication port of the Blustream Node, it automatically establishes contact with the central database and updates it. Any changes made to the tilt at the site are automatically updated when the site is polled. An additional feature of this option allows Operators, when required, to restrict change access solely to the control centre.
Interoperability is vital for this technology to flourish. Interoperability between different antenna types, between amplifiers and antennas and between site controller or communication node and antennas, is vital. Ultimately, interoperability between site programming devices and antennas to simplify the installation process is a must.
The activity between companies has increased dramatically and the emergence of an array of affordable and inter-connectable devices is sure to see a massive uptake in the remote adjustment of antenna-line devices, this will dramatically alter the way in which mobile networks are optimised in the future and will deliver significant OPEX savings to the operator.