AIRCOM

AIRCOM Gurus: What Happens To Transmission When RF Bandwidth Exceeds Backhaul?

 

The increasing popularity of smartphones is placing increasing pressure on operators’ data bandwidth. A myriad of phone applications and live video streaming are all causing networks to feel the strain. Technologies such as 3GPP HSPA and EVDO have led to an increasing consumer demand for bandwidth-hungry services that far exceed simple web browsing. Emerging 4G technologies such as WiMAX and EPS are pulling together to present a true mobile broadband experience. The capacity of these systems is growing, with the potential to be huge. Today’s peak rates of up to 45Mbps with HSPA+, is, in 4G, expected to reach up to 100Mbps DL. Even for multiple users in a single cell site, this equates to 5-10Mbps per user (downlink) and 1-4Mbps (uplink). Compared to the average fixed broadband rate of 8Mbps, this compares pretty well.

These high data rates can be achieved by applying a number of changes to the radio interface, such as introducing MIMO or adaptive modulation and coding along with higher modulation schemes, new multiple access techniques (OFDMA), etc. Yet the high bandwidth rates can become severely limited by network backhaul, leading to a notably degraded service, or potential signalling failures resulting in dropped packet calls. This is because the majority of current backhaul networks are deployed using TDM/ATM transmission techniques - efficient for voice services, but not optimal for bandwidth-hungry data services. This means that a redesign or significant upgrade of backhaul networks is having to be considered by operators, to cope with already perceivable backhaul bottlenecks.

The straightforward solution is to increase the number of leased lines and/or microwave links to provide more backhaul bandwidth. However, this approach is very costly and not really efficient for such a dramatic increase in capacity (typically a mobile broadband user requires 30x the backhaul bandwidth of a traditional mobile ‘voice services only’ user). Furthermore, 4G technologies are defined only for all-IP transport logic, meaning that the whole network would have to be transmitted over IP.

Instead, operators are looking to make their backhaul predominately not only packet but entirely IP based for the first time. This is a step change from the early GPRS backhaul support required for the first mobile packet networks back in 1997/8. Now, operators have to migrate to entirely packet switched technologies such as MPLS/IP in new backhaul deployments, not only to be able to support the new services advertised, but to make a step towards the necessary 4G upgrades for truly distributed Radio Access Networks (RAN).

This upgrade will most likely happen in phases. As a first step towards IP backhaul, HSPA/EVDO traffic can be offloaded over Ethernet transmission networks, while voice services can remain transmitted over traditional TDM/ATM networks. There is already a plethora of equipment available to support this hybrid technology approach as Multi-Service Platforms. Bridging technologies/techniques such as xDSL/Pseudowires (PWE3) can then be introduced to emulate circuit switched networks over underlying IP/Ethernet networks and allow the transmission of TDM/ATM over Ethernet where necessary.

Eventually, transmission networks will evolve to all optical/cable based solutions that support Ethernet/IP pure packet networks with traditional technologies only ever emulated as necessary for legacy systems.

Mobile operators have to significantly upgrade their transmission networks as they are moving towards 4G, as speeds are expected to be half an order of magnitude faster than today. However, known data latency issues being experienced today hint at the fact that this evolution is not happening fast enough to support even the current demands! AIRCOM is working to support customers in this evolution. Early next year will see the launch of our latest software, Conductor which tackles these complex issues bringing together mobile and transmission planning, enabling migration planning scenarios to be evaluated quickly for an optimal solution.

Y.G./G.F – Mobile Networks Systems Team

Product spotlight: CONNECT - Saving OPEX, using adaptive modulation

 
Next generation networks are fast becoming a reality. WiMAX and LTE are on our doorstep, promising to provide us with the ultimate ‘anytime, anywhere’ broadband experience. Mobile multimedia revolution, rather than evolution, is ready to rule. But we are not there yet. Mobile operators need to protect their profitability, ensuring financially viable next generation networking.

The explosion in the usage of the mobile internet means that the volume of data travelling over the whole network will reach unprecedented levels. This is not an issue in the core part of the network, where optical fibers can transport huge amount of information, but what about the network edges? Let’s take a look…

The current infrastructure to connect the core network to the base stations (backhaul) is mainly based on E1/T1 lines and microwave links. The increase of capacity over the T1/E1 lines  translates to a tremendous increase in operators’ OPEX. Therefore, microwave links are a much more cost effective and efficient means to providing a transport network. Another efficient alternative would be transporting via optical fibers, but unfortunately,  digging up half the world to install fibers is not especially feasible, even if they do offer optimum capacity.

Backhaul transmission needs to evolve to cope with the future demands of next generation networks. One ingenious new trend that addresses this is adaptive modulation (AM) in microwave networks, where the modulation order of the radio changes according to the link characteristics. In modulation, the data message is transferred over a radio signal. In order to be more efficient, we can transfer more bits at a time, considerably increasing the total amount of data transmitted at a minimal cost. And this is the key point of success for adaptive modulation; delivering more data with less money.

AIRCOM’s CONNECT microwave backhaul and transmission planning tool understands the importance of adaptive modulation and we have introduced it as one of the tool’s core features. The available schemes that the equipment operates on are defined, as well as the required throughput that needs to be delivered. By adapting the right modulation scheme for continuously varying throughput requirements, based on the operating bandwidth for all links operating in the network, CONNECT ensures that it always fulfils users needs. The average throughput is a linear function of bandwidth and operating modulation scheme. The higher the bandwidth, the higher the spectrum costs. 

 

Just work out a cost calculator for yourself in terms of spectrum - by managing the modulation alone based on throughput requirements dynamically, you will start to realize the amount of savings on licensing costs of the spectrum. This in many cases is will be in the order of $1M when managed effectively.

 

Mobile operators need to make the most out of their investment in their existing infrastructure (TDM and not all-IP), so they will be reluctant to dismiss it all overnight. And that is not all; higher order modulation schemes (256QAM compared to 8PSK) mean that links would be unavailable more often, which it is not a major problem for internet browsing, but would prove catastrophic for voice calls.

Envisioning such needs, and looking towards tomorrow’s technology today, CONNECT provides all the necessary information to a planner, enabling them to make better use of their resources, have a better understanding of their needs and to have a more control over required spending, while maintaining the required Quality of Service. In this business, that balance of control and quality is vital.

 

JR & AS, CONNECT product team.