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Efficiency

Dr John Naylon, Chief Technology Officer, CBNL

Dr John Naylon, Chief Technology Officer, CBNL

Whilst Brazil is on course to stage two major global events, there is huge potential to learn from previous events, global best practices and technologies/applications.Millions of people are expected to flock to Brazil during the summer to attend one of the most widely viewed sporting events in the world.

Spectators will be equipped with smartphones and tablets to catalogue every moment, call family and friends or share photos and videos on social media.

With Brazil going through a mobile revolution of its own, mobile broadband subscriptions have increased year on year, the 2014 FIFA World Cup could be the biggest mobile event ever held.

However, the challenges facing Brazilian operators to quickly and flexibly increase mobile connectivity are considerable – the huge strain on Brazilian mobile and internet networks will be unprecedented.

The expected surge in mobile data demand, on top of an already strained network, will require a huge amount of infrastructure and capacity planning, as well as studying lessons learnt from previous major events.

The 2012 Olympics in London, for instance, was considered the most digital Olympics ever, with its high reliance on technology for infrastructure, services and information, as well as consumption by global audiences.

There was a significant dependence on mobile data and the network infrastructure needed to backhaul the surge in traffic.

The event saw over 627,000 Facebook check-ins across the 40 plus Olympic venues.

The surge in traffic meant operators had to quickly provide multiple areas of increased mobile coverage and capacity across venues and the wider city.

At a time where CAPEX for large communication projects is limited, the demand for next generation mobile services requires innovative infrastructure which not only provides the performance needed, but can be deployed quickly and cost effectively.

An approach taken by operators during the 2010 FIFA World Cup and London 2012 was to deploy high capacity point-to-multipoint (PMP) microwave backhaul.An approach taken by operators during the 2010 FIFA World Cup and London 2012 was to deploy high capacity point-to-multipoint (PMP) microwave backhaul.

By deploying PMP microwave, operators were able to quickly, flexibly and cost effectively bring the network closer to consumers at demand hot spots (stadiums, highly populated streets, etc) and provide a seamless high quality of service.

PMP microwave creates a sector of coverage from a single hub site which can backhaul a number of cell sites.

By aggregating multiple cell site traffic to a single hub, PMP saves on the large equipment costs of traditional backhaul technologies and is able to intelligently allocate 3G, LTE or Wi-Fi mobile capacity where it is needed most.

As network challenges grow at the same pace as user expectations, cost effective technologies like PMP microwave are particularly attractive to operators where the average revenue per user is low as it delivers every bit of data in the most economical way possible.

Whilst Brazil is on course to stage two major global events, there is huge potential to learn from previous events, global best practices and technologies/applications.

Though the challenges of delivering mobile communication infrastructure for major events are significant, by utilising the best and most innovative technologies, the FIFA World Cup and Olympics will be sure to deliver victory on the track and field that the audience can share the world over.

Chris Wright, Marketing Manager, CBNL

Whether maximising the use of software defined networking, optimising transmission circuits, or introducing innovative new business cases – driving efficiencies in backhaul was centre stage at this year's Packet Microwave and Mobile Backhaul Forum.

With LTE and small cells often the backdrop, the event provided an insight as to how operators can exploit new solutions to cost effectively manage the rising tide of new applications traffic.

As event sponsors, CBNL played a leading role in discussions and have provided our event highlights on two short films.

Packet Microwave Forum 2013, Day 1: SDN for efficient backhaul and highlights

Packet Microwave Forum 2013: Day 2 highlights

Dr John Naylon, Chief Technology Officer, CBNL

One of the most common questions we’re asked by new customers is,

“How do I decide when to deploy point-to-multipoint (PMP) and when to deploy point-to-point (PTP) for my backhaul?”

This is a great question, because the two technologies are very complementary to each other. 

An engineering perspective

From an engineering perspective, in making the choice between PMP and PTP for a given link, we are seeking to maximise efficiency and utilisation of the equipment and the RF channel while satisfying a set of requirements for throughput, latency and link availability. 

In economic terms, this translates into choosing the technology which gives the lowest total cost of ownership while satisfying those requirements.

Traffic characteristics

An excellent way to make the choice between PMP and PTP is to look at the characteristics of the data traffic we want to carry. 

I’m going to consider mobile broadband backhaul traffic here, because that’s what the majority of our customers use our technology for today. 

In a future post I will talk about small cell backhaul traffic.

As ever, the NGMN has some useful information we can use, in the whitepaper Guidelines for LTE Backhaul Traffic Estimation.

This paper describes (§2.2) the initially counter-intuitive result that the peak throughput for an eNodeB actually occurs, not during busy hour, but during quiet time. This is because:

“During busy times, there are many UEs being served by each cell. The UEs have a range of spectrum efficiencies, depending on the quality of their radio links. Since there are many UEs, it is unlikely that they will all be good or all be bad, so the cell average spectral efficiency (and hence cell throughput) will be somewhere in the middle.

During quiet times however, there may only be one UE served by the cell. The cell spectrum efficiency (and throughput) will depend entirely on that of the served UE, and there may be significant variations … the scenario under which the highest UE and cell throughputs occur [is]: One UE with a good link has the entire cell’s spectrum to itself. This is the condition which represents the ‘headline’ figures for peak data rate”.

Figure 4, reproduced here, illustrates this point:

Illustration of cell throughput during busy and quiet times

The paper goes on to give the following peak and mean traffic figures for a number of LTE configurations:

Figure 5: Mean and peak (95%-ile) user plane traffic per cell for different LTE configurations

Understanding the peak-to-mean ratio

What we can immediately see from this figure is that the peak-to-mean ratios of the traffic in the dominant, downlink, direction are very large, ranging from about 4:1 to almost 6:1. 

This agrees well with measurements we see from real networks. 

For example, the following from a very busy HSPA+ network show the peak-to-mean ratio of the backhaul traffic for each node B (on the y-axis) plotted against the peak backhaul demand for that node B on the x-axis.

Peak Backhaul Demand (Mbps)

When traffic has a high peak-to-mean ratio like this, we call it “bursty”, as opposed to “smooth” when the peak-to-mean ratio is close to 1. 

Data traffic in general, for example on LANs and residential internet access connections as well as mobile networks, is bursty; and this presents a difficulty in carrying it efficiently on PTP links, as shown here:

Bursty traffic is hard to carry effeciently

The problem here is that a PTP link with a single traffic source (a ‘tail link’ in the backhaul network) needs to be dimensioned to carry the peak traffic, but there is only a single source of offered load. 

Therefore the utilisation of the link (or efficiency) is equal to the mean offered load divided by the capacity, or in other words the reciprocal of the peak-to-mean ratio of the traffic. 

So if my traffic has a peak-to-mean ratio of 4:1, the maximum utilisation of a PTP link carrying that traffic is ¼, or 25%. 

In the chart above, you can visualise this as all the white space below the red line being wasted bandwidth, which is provisioned but unused.

It’s important to say that this is not a failing in PTP systems in any way – it is simply that the characteristics of the traffic are not well suited to the static bandwidth provisioning that PTP provides.

The advantage of a PMP system is that it can serve multiple sources of offered load simultaneously. 

The bandwidth of the shared RF channel is dynamically allocated to different sources as required. 

Conceptually, then, the peaks and troughs from different traffic sources ‘cancel out’ to some extent, as we illustrate in the following live network example showing eight nodeBs being backhauled by a single VectaStar Gigabit sector.

Multipoint backhaul packet switched not circuit switched

Here we are also relying on another property of the traffic, namely that peak demands for different nodeBs do not occur at exactly the same time. 

We discuss this at greater length in The Effect of System Architecture on Net Spectral Efficiency for Fixed Services.

Liberating spectrum to meet growing capacity demands

A useful analogy here is to think about a bank with deposit accounts.

Banks operate a fractional reserve system, meaning that they are only able to repay a defined fraction of the total of deposits at any given time.

This therefore relies on the observation that, statistically, not everybody goes to the bank and withdraws all their savings at the same time.

When this assumption breaks down, there is a ‘run on the bank’.

In a similar way, we rely on the observation that, statistically, not every node B requires its theoretical peak backhaul throughput at the same time.

When this assumption breaks down, things are a bit less dramatic however – we simply discard some low priority traffic.

This is perceived (if at all) by users as a temporary reduction in internet browsing speed.

Crucially, we can dimension the system in such a way as to set the probability that this occurs to a value of our choosing.

The advantage of fractional reserve banking is that it liberates dormant capital for further investment and lending.

Likewise, the more efficient use of RF channels in PMP systems liberates dormant electromagnetic spectrum (provisioned but unused, as in the example above) for use addressing the ever-growing capacity demands of modern mobile networks.

Conclusion

In conclusion, then, some brief rules of thumb for when to deploy PTP and when to deploy PMP are as follows:

Deploy PTP…
… when traffic is smooth (voice dominated)
… when traffic has already been aggregated
… in the middle mile of backhaul
… for long distance links
… when spectrum is uncongested or inexpensive
Deploy PMP…
… when traffic is bursty (data dominated)
… to create an on-air traffic aggregation
… for tail links (last mile)
… for dense deployments
… when spectrum is congested or expensive

 

Dr John Naylon, Chief Technology Officer, CBNL

Why multipoint microwave may be one of the sharpest tools in the box

The challenge of how to backhaul outdoor small cells with the required capacity and coverage (and at the required cost) was much discussed at last month’s Small Cells World Summit.
 

But which solution ticks all the backhaul requirements?
 

My seminar at the event centred on this question and on the fact that there is no ‘one size fits all’ solution for the range of small cell network environments we are starting to see.

But this needn’t cause concern.

I’m a firm believer in the toolbox approach which addresses many of the challenges of small cell backhaul and provides operators with a great opportunity to meet their customers’ data demands and maintain revenues through an efficient deployment strategy.

As we move through small cell trials and towards commercialisation, it’s clear operators must have a variety of small cell backhaul options in their armoury.

This should include fibre (where possible) and a range of wireless technologies including; non-line of sight multipoint, e-band point-to-point and high capacity multipoint microwave - each bringing unique qualities to the table.

My presentation (downloaded a pdf here) presents an overview of small cell backhaul challenges and the role we expect each wireless technology to play.
 

 

Once small cell networks become established some interesting trends will start to become apparent in the network traffic.

It’s very likely backhaul traffic will be a lot burstier and have higher peak data rates than traditional networks, caused in part through a reduced amount of users per site compared to that we typically see on a macro cell.

This will demand greater efficiency in the backhaul if it is to meet operators’ business cases and is one of the key reasons why high-capacity multipoint microwave should be on the must try backhaul list for all operators.

The efficiency gains multipoint microwave brings through aggregating backhaul traffic make it an essential tool for small cells backhaul.

This aggregation not only provides high-capacity backhaul to meet users extreme data demands, but vitally reduces the cost per link.

 

Here's a video from the Small Cells World Summit where I provide more information.

 

Published 16 April 2012 in Backhaul, Events
Tags: 2G, 3G, 4G, VectaStar, CEPT SE19, Efficiency

Dr John Naylon, Chief Technology Officer, CBNL

Industry opens eyes to address 75% under-utilisation of cell site backhaulAt CBNL, we have a philosophy of exploiting the statistical properties of mobile backhaul traffic to build efficient and cost-effective networks.

We've made extensive measurements of 2G, 3G and 4G backhaul traffic and our most striking observation is that the backhaul peak-to-mean ratio in data-dominated mobile networks averages about 4:1.

The logical consequence - assuming you don't constrain the RAN by under-provisioning the tail links to nodeB’s (and who would do that?) - is that the mean utilisation of traditional point-to-point (PTP) microwave links is only about 25%.

So we were pleased to see one PTP vendor present data that confirmed this low average utilisation at the CEPT SE19 spectrum engineering working group meeting in Copenhagen in March.

Slide 7 in the vendor’s presentation confirmed that 60% of links in one large mobile operator's network in Europe operate at 30% or lower utilisation.

Why is that?

Well, imagine we have a nodeB with the average peak-to-mean ratio in its traffic of 4:1.

Let's say its peak backhaul demand is 40Mbps to make the numbers easy (about right for a very busy HSPA+ tri-cell).

I'm going to provision exactly 40Mbps of PTP microwave backhaul to this node B.

I know the peak load is 40Mbps so using the peak-to-mean ratio of 4:1 I can derive that the mean load is 40 / 4 = 10Mbps.

Therefore, since there is no other source of traffic on the PTP link I can immediately calculate its utilisation, which is defined as the mean load over the capacity: 10Mbps / 40Mbps = 25%.

How backhaul can improve utilisation and operator profitability

At CBNL, we wouldn’t settle for our radios transmitting idle patterns for 75% of the time, so we implement a point-to-multipoint (PMP) multiple access scheme.

This means there is more than one source of offered load for the radio link, and so we can very easily achieve much higher air-link utilisation than PTP.

This translates directly into lower spectrum lease costs and other opex savings for operators.

With rising data traffic, mobile operators will not be able to operate profitable networks with inefficiencies of this scale spread throughout their network!

It's great to see other thought leaders in the industry facing up to this issue.

Of course, we think point-to-multipoint microwave is a better solution than the peculiar asymmetric channel arrangement that certain PTP vendors are proposing - more details on that another time.