LTE – turning the tables on cable

By Charles Sturman, Senior Principal, Product Strategy, u-blox.

In our homes and offices, cabled connectivity has almost exclusively provided our access to the internet, since it originally piggybacked on the existing telephony infrastructure. Ongoing cable enhancements saw ISDN, DSL, ADSL and fibre optics offer exponential bandwidth and latency improvements, while cellular communication lagged a generation behind, suffering from bandwidth and latencies at least an order of magnitude below. In places where cellular service was necessary, e.g. to connect distant rural communities, then the relatively high price of deployment and operation came to the fore.

During the late 1990s it became clear that a fundamental move away from circuit switched communication was necessary to deliver mobile internet to the new breed of smartphones emerging in the market. This insight coupled with operators’ needs to replace falling voice revenues gave rise to the development of the fourth generation of cellular networks – LTE. Although developed to serve mobile devices, for the first time, cellular communication was capable of offering a commercially viable alternative to fixed internet access. While fibre optic cable can facilitate much higher bandwidth, the cost of deployment to individual premises coupled with typical internet use‑cases (infrequent, bursty bandwidth requirement rather than sustained high bandwidth) puts LTE in a favourable position versus fixed fibre bandwidth. The commercially prohibitive “cost‑per‑megabyte” pricing structure which has stunted the growth of cellular communication is also rapidly disappearing.

Round‑trip latency (the fixed time it takes for a remote data request to be sent and responded to) is as important as the underlying bandwidth. The current 4G infrastructure averages around 50ms, which is about the same as current ADSL internet cabling. Although a fibre optic line will get this down to around 5ms, most fixed internet connectivity today uses ADSL and real time applications, such as on‑line gaming, video streaming and VoIP, demand less than 100ms. Since the cellular network backbone is predominantly fiber based, it will be no surprise to hear that next-gen cellular (5G) is targeting 1ms latency with 10Gb/s bandwidth!

Ahead of what can truly be termed ”5G”, evolution in the 3GPP LTE specification, as visualised below, demonstrates the significant increase in bandwidth available within the current-gen. The “killer‑app” of internet driven smart phones and tablets has funded the investment that is necessary to upgrade the vast cellular infrastructure.

Although spectrum is naturally a limited resource, the increased efficiency of the newest RF modulation schemes (such as OFDM and Carrier Aggregation) has turned the tables on cable. In contrast, satisfying the rapid growth of new cabled connections is becoming prohibitively expensive to deploy and maintain. Green‑field deployment and backhaul cable replacement on land with ever higher population density and increasing environmental/regulatory considerations is becoming less commercially viable than ever before.

Any cable system suffers signal degradation, and while fibre optics significantly reduces degradation, the “holy grail” of Fibre To The Premises (FTTP) is commercially impractical for mass adoption. Numerous hybridisations have, to some degree, addressed this by providing fibre To The distribution point (FTTdp) and patching past DSL methodologies to trade distance over the last‑mile of connectivity for increased bandwidth. However, the net delivered bandwidth in these systems is an enhancement over cable, rather than anything approaching true fibre speeds.

Although it was once implausible that cellular could ever match the performance of cable networks, this is now indeed the case, with current Category 6 LTE modems providing 300Mb/s downlink and Category 9, coming later this year, providing 450Mb/s.

These so called LTE “Advanced” solutions utilise new techniques to squeeze even more out of the available spectrum, in terms of bandwidth, connection reliability and range. It should be noted that these issues are also experienced in cabled connectivity, but need different approaches to address them.

MIMO (Multiple Input, Multiple Output - multiple antennas) has always been a central concept of LTE – initially with two antennas each on the terminal and base station – as a means of enhancing signal integrity and more recently as a means of extending bandwidth and coverage. Enhanced MIMO expands this idea to utilise four or even eight antennas simultaneously to increase throughput. Beam‑forming takes the enhanced MIMO concept and makes it “smart”, exploiting an array of antennas and advanced signal processing to intelligently steer radio beams through space precisely towards the target. Further, by aggregating discrete RF bands through Carrier Aggregation into a single wider frequency band, throughput can be further multiplied. Originally only two times combining was supported, but this year has seen that rise to four times.

It’s not all about increasing bandwidth though; equally important is maintaining bandwidth at varying distances from a base station. Co‑ordinated MultiPoint (CoMP) achieves this by aggregating channels from multiple base stations to fill‑in the reduced data rate as you move away from one base station and closer to another.

Beyond the constant evolution of what we achieve via our internet connectivity, naturally lies how we access it. In our homes and offices, we’ve journeyed from all our internet enabled devices needing fixed (invariably RJ‑45) cabled connection, to alleviating device cabling constraints via a local WiFi router. However, we are all familiar with WiFi’s own distance constraints, which lead to losing connectivity and then hunting for an alternative connection point, only to find that it is locked, or requires credit card details. With today’s LTE bandwidth, coverage and low cost, people tend to stay with the cellular connection longer. Increasingly, ISPs that once only offered fixed‑line connections, are now offering internet, TV and cellular connectivity all under one subscription plan, allowing seamless migration between indoor fixed and outdoor wireless internet.

While our insatiable appetite for internet use continues to drive bandwidth growth, other new applications and technologies drive the progression towards everything becoming connected (Internet of Things: IoT). Our new “smarter” homes are adopting low power sensors, voice activation and Artificial Intelligence clients. Huge advances are being made to provide low power direct cellular cloud access via Narrowband IoT (NB‑IoT) in order to connect these devices.

An interesting question is how the “IoT cloud” will interact with the broader internet. In my view, the smart home of tomorrow will continue to utilise a local internet access gateway, while also supporting direct IoT cloud connectivity. For example, energy companies providing smart energy meters will likely prefer “always‑on” remote access via cellular than leave the connectivity to the whim of the homeowner controlled gateway.

Even being at the forefront of wireless and cellular technology, u‑blox cannot predict the depth and breadth of exciting new use cases that emerge for IoT every day. Our broadband connectivity solutions, comprising high performance pre‑certified LTE CAT 6 modems and pre‑integrated with local connectivity technologies, such as WiFi and Bluetooth, cover every conceivable use case while slashing time-to-market and development risk. Leveraging our partnership with Intel, u‑blox exploits the cutting‑edge functionality available within the latest LTE chipsets to produce an optimised base platform for consumer end‑point devices, gateways and routers.

Courtesy of u-blox.