IP based backhaul requirements push for Synchronisation changes in GSM and UMTS Base Stations
Introduction
Technology and user requirements in the mobile arena are racing to deliver high speed data services in addition to traditional voice. The primary driver for this is to ensure repeat subscription, new business and upgrade of service subscription utilising the new technologies now available.
In order to achieve this, higher data transfer rates are needed, and most importantly operators will require much larger backhaul bandwidth; as such operators are developing new methods of high capacity backhaul that must be more cost effective than traditional methods. The main driver is to maintain quality of service in a more effective manner.
Synchronising GSM / UMTS - How it's done now
As a result of this evolution, synchronisation methods for GSM and UMTS networks must evolve. In traditional GSM and UMTS networks base stations must attain a local synchronisation reference quality of +/- 50 parts per billion (ppb) this is assumed over a ten year life cycle of the synchronisation device.
If base stations do not achieve or supersede this quality then the end user will experience quality of service problems such as call dropout, handover problems and poor data service / transfer.
The historical method of achieving synchronisation quality within the GSM environment (in particular the base stations) was to use a low quality oscillator retimed from either a T1 or E1 backhaul line. This was known as recovered clocking and with out this method of synchronisation the network would not operate due to the instability of free running oscillators.
GSM / UMTS - What's next?
IP is rapidly becoming the predominant protocol of data transfer in the modern world and the GSM / UMTS markets are not an exception to this. Increasingly transport networks are moving to an IP based topology which would offer mobile operators a cost effective high capacity backhaul service.
The problem
With the move to IP based high capacity backhaul systems historical GSM / UMTS synchronisation methods such as recovered clocking cannot be employed, due to the IP based environment.
In order for operators to meet the required synchronisation quality of +/- 50 ppb an independent synchronisation method must be utilised at the actual base station.
What's going to happen in historical GSM base stations?
There is a synchronisation problem for legacy GSM base stations that have previously utilized clock recovery from T1/E1 leased lines, often provided by fixed operators. The change of backhaul to CES (Circuit Emulation Services) such as satellite transport will require a synchronization reference source placed at the base station to deliver the required quality of synchronisation.
There are two ways to achieve this:
1. Utilise an external GPS clock to externally time the base station equipment.
2. Use a GPS based retiming device
Until recently the synchronisation of GSM base stations has been somewhat overlooked or taken for granted the retiming solution was sufficient.
However, now that backhaul transport is rapidly changing and the requirement s different, the base stations can no longer rely on recovering synchronisation from the network.
It is now vital that operators and manufacturers meet the challenge to ensure that the synchronisation plan meets the requirements of the user to ensure business security and be ready to provide the next generation of mobile services.
E-mail: info@horsebridge.net
Oscilloquartz - OSA453x GPS Receiver Range
The existing and emerging standards in the world of mobile telecommunications and digital broadcasting demand the highest quality of synchronisation. A proper timing signal therefore becomes more and more important for media Centers as well as for cellular networks where location services such as E911 will have more importance.
The unique architecture of the OSA 453x Series is designed to maintain the strict CDMA holdover specifications. The OSA 453x Series are also a natural choice as a synchronisation source for UMTS, WCDMA and cdmaOne, as well as GPRS, CDMA and TDMA base station and mobile switches. Their 1 PPS and 10MHz outputs make them ideal for synchronising DAB/DVB equipment.
Common features
All models provide standard 1 PPS, 10 MHz and TOD (Time Of Day) outputs referenced to UTC1. All models include a highly accurate ovencontrolled oscillator, which filters the reference signal and provides a holdover quality comparable to that of an SSU in case of loss of external reference.
Oscilloquartz OSA 4530/1/2 GPS
The OSA 4530/1/2 GPS are GPS Receivers providing E1/DS1/2.048 MHz outputs according to ITU-T G.703-X. Models 4531/2 also accept an auxiliary E1/DS1/MHz reference as a robust alternative to GPS.
Oscilloquartz OSA 4533/4 GPS & OSA 4535/6 RTM
The OSA 4533/4 GPS and OSA 4535/6 RTM are Re-Timing Modules that re-time one E1 or DS1 traffic signal. Models 4533/4 take GPS as reference, while 4535/6 smooth out timing impairments from the traffic signal and therefore need no external reference.
Features:
• Fully compliant to ITU-T G.811 / Stratum 1 when locked to GPS
• Integrated high stability holdover functionality < 2x10-10 /day
• Holdover compliant to ITU-T G.812 type I, V, VI
• Output 10MHz, 1PPS
• Various outputs types (E1 / T1 / 2.048MHz)
• Re-timing of one E1 / T1 traffic signal
Benefits:
• Low cost GPS receiver module
• Compact reference for Cellular networks application like UMTS, GPRS and CDMA
• Re-timing of traffic, e.g. for transit switches
• Optimum clock for Wireless and wireline telecom sync requirements
• Ideal source for specialised ATM and LAN/WAN applications
• External input filtering capabilities
Horsebridge Services:
As well as supplying the OSA453x range, we also provide a host of supporting services, including:
• Installation.
• Commissioning.
• Technical support.
• Spares support.
• Product training.
If you would like to know more about the OSA453x range, then why not contact us now.
Oscilloquartz OSA453x Datasheet
“We have worked very closely with Horsebridge for a number of years and
continue to experience the highest level of pre- and post sales support. With their varied skills and knowledge base, Horsebridge are able to provide a totally joined up solution from the design stage through implementation to after sales support, giving Jersey Telecom the confidence that projects will run smoothly and within agreed timeframes. Furthermore, Horsebridge's team of technical experts are highly responsive to our urgent needs enabling us to focus on our daily core business requirements." 
“WiMAX networks issues can often stem from poor synchronisation — networks tend to be synchronised at the core, but not at the edge. As the industry experts in this space, Horsebridge were highly responsive to our needs by offering one of the first cost-effective carrier class solutions for enabling accurate data transmission across the entire metropolitan area. Through this partnership we will be able to ensure quality of service across the network while reducing the risk of any service interruptions to customers from interference.” 
“The content structure was appropriate to our requirements. The course content was clearly explained and the training staff knew the subject deeply, hence the synchronisation knowledge was strengthened, even for the more experienced participants. The practical part of the training was very useful as it focused on real case scenarios and our customers network. The overall rate for the training is very good, however I must say that for some people it was excellent.” 
"I have found that the services provided by Horsebridge have at all times been of the highest standards, their attention to detail and genuine willingness to help the customer are, I find, a pleasant surprise in these days of take the money and run." 
