Increment of average revenue per user (ARPU) always expected by Mobile Network Operator (MNOs), also increase the number of subscribers for services and for ways to increase customer loyalty. To accomplish these goals, MNOs need to implement the optimal network topology, with reliable and proven high availability. The challenge, rest in achieving rapid and cost-effective service expansion while keeping up with the newest technological and social trends.
Satellite communication has become a solution of choice for an ever-growing number of backhaul deployments, particularly in rural environments where alternatives are impractical, The requirement for high-throughput broadband data traffic goes hand-in-hand with the remarkable and ongoing increase in speed and capacity. 3G/LTE networks are being build to support this need and they call for an implementation that allow data transfer at peak rates of more than 100 Mbps.
For satellite communication to deliver the optimal cellular backhaul solution, it is important to understand the differences between the traffic patterns of traditional GSM networks and high-speed 3G/LTE networks. Analysis of network behavior shows that peak performance (> 100 Mbps) is significantly different than average traffic per user (< 1 Mbps). This behavior encourages sharing of the satellite bandwidth resource among multiple cells and is the only way to achieve a viable business case.
Satellite Backhaul Access Scheme
Efficient satellite backhaul implementation must account for many factors. A careful analysis needs to examine network usage and to determine the access scheme that fills the need cost effectively.
Single Channel Per Carrier (SCPC)
The SCPC solution uses modems at both ends of the link, occupying the maximum-needed bandwidth permanently at each cell, regardless of actual momentary traffic demand. In this case, a continuous modulated carrier is used, which runs at a fixed speed all the time, in both directions.
When traffic demand is stable and matches the allocated bandwidth, SCPC transmission is highly efficient. This is often the case when the quantity of active subscribers served by a specific cell is quite large. In this situation, in conformance with the law of large numbers, that the deviation from average usage is small. This result in stable demand, which indeed justifies fixed, dedicated bandwidth.
Time Division Multiplexing / Time Division Multiple Access (TDM/TDMA)
Another access method is the time division multiplexing (TDM) technique, which allocates bandwidth to a specific cell in response to traffic demand. The hub transmits a common, statistically multiplexed outbond (TDM) signal to all remote cells. In the inbound direction, the bandwidth is assigned on demand, allocating timeslots to sites as needed via time division multiple access (TDMA).
The hub continuously monitors the traffic generated by each cell, allocating bandwidth from a common pool to each VSAT according to real-time demand. Thus, each VSAT is allocated more or fewer timeslots, depending on the traffic dynamics in each cell.
Shared TDMA or Dedicated SCPC for GSM Networks?
For GSM Networks, there is no absolute right or wrong answer regarding which access scheme to use. The scheme depends on what is the most economical solution to meet the individual network's needs.
When designing a satellite backhaul, the decision made on whether to implement a network system that uses time and frequency sharing schemes (TDMA), or one that uses dedicated point-to-point channels (SCPC). Each of these access schemes has its own benefits.
In cases where the cell activity factor is high and stable, it is better to use dedicated SCPC link. For location where the network traffic is continuous, with high throughput, allocating dedicated bandwidth resources with SCPC is more advantageous.
However, when the traffic pattern is variable and the difference between the peak demand in particular cell varies greatly from the average, it is prohibitively expensive to use dedicated link. In this situation, sharing the satellite bandwidth resource among multiple cells is much more economical. Networks that operate in TDMA mode take advantage of the dynamic nature of the traffic and statistically multiplex between cell sites. These networks allow bandwidth resource sharing, which can offer service providers reduced operating expenditures (OPEX) advantages.
The Feasibility of 3G/LTE Satellite Backhauling
The need for faster internet access via mobile devices is driving the integration of 3G/LTE into existing networks. Technical, social, and business changes are accelerating the adoption of 3G/LTE networks to the most remote locations.
Satellite backhauling has always been the only feasible way to reach such areas and must now stand up to the high-speed network challenge. MNOs must able to provide high performance as well as to ensure an enhanced user experience, essential security, quick deployment - all within the envelope of a justifiable business case.
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