How Fibre And Wireless Networks Are Converging At first sight, a mobile network and a modern, optical fiber-rich, fixed line network have little in common. They might be seen as competitors. After all, we hear regular stories of consumers "cutting
the cord" and meeting all their voice and basic data needs with their smart phones. In fact, the opposite is true - the growth in data volumes that need to be transmitted quickly around the "mobile" core network cannot generally be met through mobile technologies. Essentially, this means that the core of a mobile network is made up of fixed line, usually fiber, connections. The anatomy of a wireless network Before we look at how fiber and wireless networks complement each other, it is worth taking a step back to look at wireless technology overall. Mobile phones transmit and receive signals in the microwave portion of the electromagnetic spectrum, specifically in the region 872 to 960, 1710 to 1875 and 1920 to 2170 MHz in the UK. Just below that frequency range TV broadcasts are carried and at higher microwave frequencies radar, satellite communication, and specialized applications operate. This means there is limited capacity for onwards transmission of mobile telephony or data over the electromagnetic spectrum, even if it were to be a technically efficient medium. Rolling out 4G networks has been the major infrastructure project for wireless operators over the last five years, with LTE (long term evolution) prevailing over the competing WiMax technology. Both technologies are IP-based, multiple input and multiple output (MIMO), and use a form of OFDM modulation. But LTE technology is now proven to provide higher speed service to customers, in both senses of the word: line rates are higher, but reception is still good when the customer is in a rapidly moving vehicle (such as a train or car). The inherent issue with 4G of any variety is that, as a general rule, as bandwidth increases the area covered by an individual cell goes down, meaning more masts are needed. As mast numbers increase, more cable routes, and hence more cable, are required. As a result, an entirely new product category has arisen: "antenna cables" that combine optical fibers with power cables to feed the baseband unit at the foot of the mast. In most instances, the optical elements in the antenna cable are separated from the power feed and jointed to a conventional outside plant optical cable. Another deployment method that is growing in prominence is DAS (distributed antenna system). This uses a number of lower-powered transmitters rather than a single higher powered one, giving greater efficiency (less power consumption) and greater coverage. DAS works particularly well within urban areas, where increased capacity is required, as equipment can be mounted on existing street furniture, such as street lamps or signs. It can also be used within buildings that have poor external mobile reception, with optical fiber cables used to distribute the traffic from a roof antenna to sub stations within the building. Meeting growing capacity needs So how big is this requirement for backhauling mobile data over fiber networks? Back in 2012, Cisco forecast that the growth rate in mobile data between 2011 and 2016 would be 78 per cent CAGR. In fact, in 2014, the growth rate was 69 per cent CAGR, which is not far short. Capacity requirements are a function of individual needs, multiplied by the numbers seeking that service. Demonstrating growth, in 2014 global mobile subscriptions passed the two billion mark, and this year they have exceeded seven billion. By the time you read this, there may well be more mobile phone subscribers than there are humans on planet Earth. So, since we have at least one mobile connection per person, have capacity needs peaked?. For those concerned with creating fiber networks, looking at the figures more deeply reveals that is not the case.