YateBTS in the age of IoT

These days, everybody’s talking about the Internet of Things. And it’s no surprise that everybody loves it; from operators, who see a chance to attack new markets and better retain customers, to urban consumers who can connect a whole range of devices to an app on their smartphones, and farmers who can use technology to optimize their activities and maximize production.

Bringing IoT to such different audiences while maintaining a high quality of service and an efficient use of network resources is a challenge for most carriers’ current infrastructure capabilities and cost strategies. In fact, a critical concern when it comes to creating IoT infrastructure for new areas is laying the ground for that infrastructure – that is, mobile network coverage.

The number of IoT applications designed for farming and livestock breeding is on the rise, but their actual penetration in rural areas is limited to regions with existing GSM/GPRS infrastructure. Remote and rural areas offer mobile operators enticing prospects not only in terms of IoT coverage, but also in terms of connecting these new customers to their entire range of services such as voice, SMS, or data. But due to the high investment requirements for equipment, civil infrastructure, or maintenance, operators are still reluctant in building mobile networks in there areas.

The success of carriers setting up new networks in remote locations depends greatly on keeping investment and operational costs down, as well as on basing their network equipment choices on redundancy, power efficiency, and flexibility. A reliable IoT infrastructure amounts to operators providing continual service, seamlessly, and in very variable weather and terrain conditions. The geography of each area and the specific needs of communities influence every decision going from civil infrastructure to power supplying and equipment maintenance. In areas with low infrastructure where grid power isn’t available, for instance, carriers must rely on alternative power sources to successfully deploy new networks.

blog_iot_2015-5-26_version2.1

YateBTS-powered IoT applications

A base station like the YateBTS SatSite offers a reliable and flexible solution for carriers to bring mobile coverage to remote rural areas. SatSite is a 2.5G low-power, lightweight base station that allows it to be easily installed anywhere from hill tops to outlying crop fields. Practical for lightweight cell sites, it can be operated in single or three-sector sites using a single solar panel. This generates a substantial reduction in operators’ initial investment costs but also in operating cell sites in the long-run.

SatSite’s low operating costs make it a particularly suitable solution for small farms and rural households, where resources are more scarce and used less efficiently. Access to IoT applications can support these communities in rendering farming activities more productive and sustainable. The flexibility of SatSite’s architecture suits the requirements of specific IoT solutions. Used for any range of applications and devices, from water pumps and soil measurement sensors, to herd tracking and monitoring, SatSite optimizes resource allocation to allow carriers to efficiently adapt their networks to the specific demands of each location.

In rural areas, access to IoT infrastructure can make it possible to attain better farming results, optimize productivity, and increase the overall quality of life. Basic mobile services can create new standards for health care, education, as well as social and economic development of these areas. Operators can play the leading role in this process, provided that their decisions successfully combine cost effectiveness for themselves, and service quality for consumers.

OFDM – the science behind LTE

No one wants the kitten video they’re watching on Youtube to stop and reload endlessly. We all want to send big chunks of data very fast, while still keeping the integrity of said data. Nevertheless, the faster you send data, the more likely it is to experience transmission problems, especially due to interference or weak signal.

OFDM (Orthogonal Frequency Division Multiplexing) is the radio science behind huge bandwidth capabilities we see in LTE. OFDM splits data into small sub-carriers, also known as data streams, on neighboring frequencies, over a single channel. It allows sending more data than through single carrier modulation techniques, and at a higher rate. OFDM also handles phenomena such as interference, noise or multipath significantly more efficiently than other modulation methods.

How it works

The following explanation is for non-engineers and is meant to shed some light on OFDM, so keep in mind that we are leaving out many details that are not critical for understanding what OFDM is or why we use it.

We’ll use a theoretical example: a bandwidth of 1 MHz and round numbers, which are easier to remember and apply to real-life scenarios.

Traditional single carrier modulation uses only one frequency to send the bits, as seen below.

SingleCarrier

In OFDM, the bandwidth of 1 MHz band is split into, say, 1000 sub-carriers of 1 kHz, and each of them sends one symbol per millisecond.

OFDM

Next, OFDM uses the FFT (fast Fourier transform) algorithm and its inverse to effectively retrieve the original data bits from the symbols and vice versa.

Last, but not least, OFDM has a special property called orthogonality, which essentially means that sub-carriers are spaced in such a way that they only partially overlap, as the peak of each sub-carrier intersects the zero crossing of the neighboring sub-carrier. This characteristic is perfectly illustrated in the image below, where you can see 5 of the 1000 1 kHz sub-carriers in the frequency domain, in a single channel.

Orthogonality is what allows us to pack sub-carriers really tight, without wasted frequencies between them as in traditional cases, which require using guard bands.

ortho_ofdm

Let’s go back to the example used earlier. The data rate obtained using OFDM is the same as in the case of single-carrier modulation, so you might wonder why we use it so enthusiastically in LTE, which is what we’ll explain below.

Effective against multipath propagation and interference

Multipath propagation occurs the moment a radio signal bounces-off obstacles that appear in its path: water sources, hills and mountains, buildings, trees etc. Multipath causes the transmitted signal to be sent on two or more paths to the receiver, making it difficult for the receiver to interpret what it receives. Only some frequencies are prone to experience multipath. In single carrier modulation systems, it has a damaging impact throughout the whole frequency and affects all of the data symbols.

SingleCarrier_multipath

Take a look at the image below: only one carrier experiences multipath, but since all sub-carriers transport redundant copies of the sent symbols, data loss is minimal.

OFDM_multipath

OFDM is also effective against interference because only some of the data streams will be affected by this phenomenon and data can be more easily recovered with redundant error-correction coding.

Spectral efficiency

When using OFDM, LTE can tailor the modulation to make the best possible use of the available radio path to and from the UEs. Because of the OFDM carrier structure, LTE can take advantage of the changes in channel conditions and uses different modulations depending how close or far the UEs are from the transmitter.

Because it uses OFMD, LTE can dynamically change the symbol alphabet, depending on the radio conditions, for each individual sub-carrier. For example, if you’re sending data close to the transmitter, LTE will apply a 64-QAM modulation scheme, that is 6 bits/symbol. But if you are moving further from the transmitter, and the radio conditions are unreliable, LTE will dynamically adapt to either 16-QAM or QPSK, sending 4 or 2 bits/symbol. In extreme cases, LTE can even use BPSK (1 bit/symbol).

Some disadvantages

OFDM also has its downsides.

OFDM has a high peak-to-average power ratio, and requires a highly linear and oversized power amplifier that usually has a low efficiency. In the image below, you can see a typical OFDM peak-to-average power ratio. This occurs because multiple sub-carriers with different phases combine constructively in the time domain.

Typically, to obtain a 5 W average output power, an OFDM system requires a 100 W power amplifier, representing an increase by a factor of 20 from the actual 5 W output. Otherwise, the distortion is far too destructive to allow OFDM to function normally.

peak-to-noise_power_ratio

OFDM is also very sensitive to Doppler shift. This phenomenon occurs when the UE is moving, thus making the frequency of the signal received different from the frequency of the initially transmitted signal. Among its effects in OFDM, Doppler shift deteriorates synchronization, data recovery, and destroys the orthogonality of sub-carriers.