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The introduction of HSPA, WiMAX and LTE radio access technologies has resulted in an explosion in bandwidth requirements on the backhaul links from base stations to the core of the network. According to a recent Infonetics Research report the number of mobile broadband users has doubled over the past year, reaching 250 million subscribers worldwide in March 2009. Bandwidth consuming applications on iPhones, Blackberries and other smart phones are growing at annual rates well in excess of 100 percent and continue to drive new demand.
However, the backhaul spectrum is a non-renewable resource – when it is consumed there is no more. In North America this has not yet become a serious issue; however, in some markets congestion is limiting the availability of path and frequency combinations. Certainly the most desirable frequencies (11, 18 and 23 GHz) are in demand. While significant spectrum is available in the higher frequency bands, it is difficult to get the reach required to interconnect the base stations in these bands.
European carriers, in particular, are facing significant capacity crunch and spectral efficiency challenges. Explaining that limited spectrum and spectral congestion were key issues Solheim told Microwave Journal, “For a long time European regulators have recognized that the spectrum is a non-renewable resource, so licensing regimes have been geared towards preserving that spectrum. Because of the pricing regime and the usage patterns of microwaves European operators are looking at either new spectrum or ways to use their existing spectrum more efficiently.”
He elaborated, “One of the problems that carriers are facing is that as they increase the capacity on the microwave backhaul they can only do so much – going to higher modulation, or adaptive modulation to get higher throughputs over the existing infrastructure but eventually you hit a wall. A lot of the last mile links have been connected with 7 or 14 MHz channels, which can typically deliver a few tens of Mbits over conventional systems.
“What DragonWave has done is to address the fact that in order to deliver the capacities that are needed in those channel sizes; you need to get a factor of two improvement in the spectral efficiency of the product. We have done many things – higher modulation rates, cross-pole interference cancellation to allow true multiplexing, adaptive modulation – and then we have added a suite of baseband optimization techniques that take a look at lossless compression, etc. So, using conventional microwave techniques we can get up to about 100 Mbits out of a 7 MHz channel and using baseband techniques we can get almost 200 Mbits out of that baseband channel.”
The company’s new product that delivers this performance is the Horizon Quantum packet microwave backhaul system, which builds on the previous generation Horizon Duo, which delivered capacity of 1.6 Gbps per link. Horizon Quantum adds to this the Bandwidth Accelerator feature, delivering up to 4 Gbps per link or 8 Gbps per ring.
The system delivers several other technical and operational advantages, including the use of XPIC that minimizes spectrum utilization and Hitless Automatic Adaptive Modulation (AAM), which delivers high capacity on longer links without the need for larger antennas, thus reducing antenna lease costs. For the most challenging links, space and frequency diversity can be used to achieve the required availability. This capability not only matches the needs of evolving 4G network deployments (both in terms of capacity and cost per bit), it does so without increasing the OPEX from antenna and spectrum lease.
In addition to the capacity increase, Horizon Quantum has been designed with the needs of next generation IP networks in mind. With support for network synchronization through Synchronous Ethernet and timing over packet (1588 v2), it meets the requirements of existing 2G and 3G base stations as well as the emerging 4G base stations, resulting in a seamless evolution to new services.
Solheim elaborated, “Certainly, LTE networks make addressing the issue of making better use of the spectrum unavoidable. However, this technology also has merit for existing network deployment, network upgrades or even just the pressure on operators to reduce their operational costs.”
Horizon Quantum also integrates Ethernet switching and nodal intelligence, so that packet-based traffic can be interconnected and routed without the need for additional third-party equipment. Eliminating boxes from the network reduces equipment cost and simplifies management and operations.
From an operations perspective, there are a number of features to simplify installation and maintenance. For instance, increased loss compensation in IF cable allows the use of smaller, cheaper and lighter cables in most installations and the ODU is equipped with an orientation sensor to allow the operator to immediately determine which polarization alignment has been installed. Maintenance is simplified by the support for advanced Ethernet OA&M features such as 802.1 ag and 802.3 ah for fault isolation and neighbor discovery.
The Horizon Quantum packet microwave backhaul system has been undergoing field trials in North America since late 2009, while in Europe field trials began in Spring 2010. During these trials Solheim envisages that European operators will see major benefits. He elaborated, “A whole new realm of possibilities is opened up. Instead of operators having to redesign their networks, go back to their regulators and try to re-engineer their spectrum allocation in the backhaul segment, they can simply deploy new equipment and upgrade the technology to LTE-style capacity without having to re-engineer and deal with all of the churn.”
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