GPS Solutions
Many of the world’s most time-sensitive applications — like mobile backhaul, network synchronization and military communications — obtain precise time from GPS, a system located over 10,000 miles away in medium Earth orbit. Symmetricom makes GPS synchronization easy thanks to our in-depth knowledge of both GPS timekeeping and the requirements of applications that rely on it. Understand for yourself the key principles driving successful GPS time-synchronization technology — and how applications and users benefit.
Wireless backhaul is shifting away from traditional TDM (T1/E1) to Ethernet IP-based backhaul. Cost is the key motivator as mobile operators need to scale economically with growing bandwidth demands. Packet-based backhaul has clearly emerged as the optimal solution, but this change takes away the TDM backhaul which served as a reliable frequency source. This paper discusses the timing and synchronization technologies that address the challenges in moving from TDM to IP-based backhaul including IEEE 1588 Version 2 Precision Time Protocol (PTP), free-running atomic clocks (rubidium oscillators) and GPS based timing solutions as well as the various advantages and disadvantages of each.
Racing ahead in the deployment of 3G (3rd Generation) wireless networks and services, carriers often give minimal pause to the concern for improving subscriber satisfaction through improved reliability of essential voice calls. The net result of this hurried evolution has been the failure to stem the churn of subscribers leaving one carrier to join the next.
The LORAN-C network is being recapitalized to serve as a backup to GPS for navigation and timing. This paper begins with a short overview of the LORAN-C recapitalization project with an emphasis on timing enhancements at the transmitting stations. A description of the commonview LORAN-C test network follows. Data collected in Boulder will be corrected via commonview using a near field station and a far field station. Results will be analyzed to determine the dependence of time recovery precision on distance.
This paper describes a connected element interferometer that has been developed and is operating with collection elements in Tucson and Phoenix with a separation of 180 km. Coherence between the collection sites of better than 50 picoseconds is achieved through two way time transfer over a commercial fiber optics link. The description of hardware and software implementation, as well as measurement results of several operating satellites, are presented.
Responding to consumer demand, service providers are expanding and upgrading their telecommunications networks at a phenomenal pace. As these networks grow they also need to ensure the non-stop availability of their timing and frequency synchronization reference, commonly known as a "Primary Reference Source" (PRS) to maintain Quality of Service (QoS), avoid dropped calls, support video streaming services, and enable LBS applications such as 911 calls. Carriers migrating to packet-based transport, however, lose ubiquitous access to the legacy TDM reference inputs. There is therefore a compelling need for a stable, cost-effective, and robust packet PRS that will provide synchronization for packet networks.
A single frequency network (SFN) enables highly efficient distribution of digital content over a wide area. Easier, faster and less expensive to service a geographic area from a grid of transmitters than using a web of copper or fiber, SFNs address the need to bring high-quality video and audio services to mobile users – with a network that can serve all users. This white paper discusses pervasively distributed synchronization that is both highly precise and reliable as a key operational requirement of SFNs as well as the technique used to send data over the airwaves – coded orthogonal frequency division modulation (COFDM).
This application note focuses on the history and need for SAASM. This is of particular importance because as of 1 October 2006, all newly-fielded Department of Defense GPS systems will use SAASM compliant Precise Positioning System (PPS) devices. Procurement of non-SAASM GPS user-equipment will be disallowed unless wavered.
GPS receivers have been widely used in communications infrastructure to provide precise time and frequency required to synchronize wireless base stations to ensure seamless call handoff, quality streaming video and location based services such as car navigation systems and most notably E911 services in the US. However, recent events have shown that GPS is susceptible to interference from deliberate spoofing and jamming techniques which can seriously disrupt or even completely disable GPS dependent applications and natural outages as with urban canyons.
