(To appear as an Editorial in IETE Technical Review, July/August 2015 issue.)
Today’s mobile devices (for example – smartphones, tablets, smart watches, smart bracelets, smart glasses etc.,) have a number of sensors embedded in them such as an accelerometer, compass, gyroscope, proximity sensor, and ambient light sensor, GPS sensor, barometer, step detector, step counter apart from the usual camera and the microphone. These sensors enable us easy access to motion data, ambient light strength, audio records, and the image of an ambient environment and so on, making our lives more comfortable and smart . As technology advances more sensors will be integrated into these mobile devices. However, further innovations can be slowed down by two problems: (i) the computing and storage limitations of the mobile devices and (ii) the cellular network constraints.
Let us understand the first problem first. Since mobile devices have limited memory and computing resources, it is better to transfer these tasks to a cloud computing environment through a network interface . After performing the computationally intensive tasks, the cloud server can return the information back to the mobile device. This is a clever idea since it will also save the mobile device from draining out its battery since the mobile device does not have to do the computationally demanding tasks. If a large number of people use these mobile devices, which will be the case in a few years, the amount of data the cloud servers need to handle can become enormous. The technique that comes to our rescue in analysing and processing such huge data, which has variety, velocity and volume, is called Big data analysis. Future mobile devices, therefore, have to constantly keep talking with the cloud servers to transfer the data generated through their sensors and this data need to be processed and analysed using Big data analysis .
Let us look at the second problem. This big data from mobile devices has to travel back and forth between the mobile device and the cloud using several network options available to us such as WiFi, cellular, or other network interfaces. Network bandwidth will, therefore, become the biggest challenge to be overcome. Network congestion in the existing network technologies (3G/4G) and the resulting drop in data transfer speeds has already become a major concern. We, therefore, require a different kind of network infrastructure which can support this massive data and its propagation without any latency.
There is an additional trouble. Apart from the data generated by the mobile devices, the next source of enormous data will come from the smart cities and smart homes that we wish to build . In a smart city, we need to provide e-governance which is expected to be not only easily accessible but also transparent and fast. But that is only one aspect of being a smart city. Energy and water conservation, efficient waste disposal, city automation, seamless facilities to travel and affordable access to health management systems are essential parts of a smart city. Traffic and weather also need to be monitored intelligently. Smart cities should be able to respond quickly to emergencies. Smart cities will also house smart energy aware homes with an ability to intelligently monitor and control lighting, security, and metering of power usage and generation. All this will require deployment of a large number of wireless sensors and devices which will generate a massive data. Handling this unprecedented data from the sensors and the data transmission between the devices and the cloud server requires a disruptive wireless technology . That is the reason why we need the fifth generation (5G) networks with speeds an order of magnitude larger than that of the existing networks. This is required to handle the data traffic volumes which are expected to increase by a thousand fold by 2020. A smart and intelligent globe is not possible without the 5G networks. Let us understand briefly about what makes the 5G networks achieve this objective of building an intelligent human society.
5G networks will have a huge band of spectrum, ranging from 30 GHz to 300 GHz since they use mmWave technologies. The wavelength of the signals in this technology is between 1 and 10 mm. This permits us to shift the wireless transmissions from the crowded spectral band of present generation wireless networks to a different band of spectrum . However, waves in this band can easily be attenuated due to environmental factors. Therefore, mm waves are ideal for short-distance communications with the benefit of re-usage of frequencies in the mmWave band minimizing the problems of shortage in spectrum.
Another departure in 5G networks, compared to the conventional cellular networks, is the deployment of massive multiple-input–multi-output (MIMO) or ‘massive MIMO’ systems. Let us first understand the meaning of MIMO. When a radio wave bounces back and forth from walls, ceilings and other physical objects and reaches a single antenna at different times and angles, it can result in interference and affect the data transfer speed. However, in massive MIMO systems this property of radio waves is better utilized by using many smart antennas which act as multiple transmitters and receivers. This will enable us to transfer more data at the same time resulting in higher speeds . The conventional MIMO becomes massive MIMO when several hundreds of antennas are deployed to serve tens of users simultaneously. A massive MIMO is upwardly scalable since by using a large number of antennas, throughput can be increased, radiated power can be reduced, and user experience in a given service area can be enhanced by a manifold, all using simple signal processing .
5G networks will employ new ways of carrying data. Even when the data becomes massive, users want faster data speeds. But this is related to the cell size, that is, the area covered by a cellular network. Depending on the area of coverage, cells are classified as Microcell (< 2 kilometres), Picocell (< 200 metres) and Femtocell (about 10 metres). One way to increase the data speed is to reduce the cell size so that cell capacity is shared by fewer users enabling them to transfer data at higher speeds. A future wireless network should be able to seamlessly interact with different cells and distributed antenna systems to enhance the cell coverage and delivery speeds. Such a network, termed as a heterogeneous network (HetNet), is the heart of 5G networks in which data transmission rates will vary widely (10 kbps to 10 Gbps), accepted delays can range from a fraction of a millisecond to a few seconds and online access requests could be from a few hundred to several million requests . Unlike the conventional single tier wireless networks, the HetNet is, therefore, multi-tier in nature with an ability to function efficiently across multiple nodes with different transmit powers, coverage areas and radio access technologies (such as Bluetooth, Wi-Fi, 3G, and 4G or LTE ) .
While 5G networks provide ways to meet the future data volumes of a networked society, we do need to overcome an important challenge. When every device that can be connected to the internet is plugged to the 5G network, it leads to what is known as Internet-of-Things (IoT) . If the devices in IoT are close to each other, the data traffic does not have to go through the base station reducing the burden on the cellular networks. Therefore, device to device (D2D) communication will be an essential part of IoT. However, as the devices connected to the wireless network may run into more than a 50 billion devices in near future and a majority of them may have to communicate not only among themselves but also with the cloud server, energy requirements will become a serious issue. The 5G networks need to be run in a cost-effective and sustainable manner since their contribution to the global carbon dioxide (CO2) emissions cannot be allowed to increase from the present levels. . In addition, if energy requirements are not contained, the user tariffs can increase and the costs for running the networks will become untenable to the network operators making the business less attractive. 5G networks, therefore, should be energy efficient by increasing the number of bits that can be transmitted for each joule of energy consumed. But this is easier said than done .
As 5G networks become ubiquitous in our lives in future, securing massive amounts of data, which could be confidential and very sensitive, from eavesdroppers is another challenge that needs to be addressed. The designers of 5G networks need to provide unsurpassed security to the data that seesaws through these networks . Otherwise, entire cities or security installations can be brought to a standstill.
As the human race embraces the massive data centric living, the unique features of 5G networks (use of small cells, device-to-device communication, exploiting the mmWave frequency spectrum with GHz bandwidth and off-loading the computational intensive operations to cloud servers) will make the 5G networks an inevitable choice of our future cellular communications systems. How quickly we can build smart cities consisting of smart homes and smart individuals is, therefore, closely tied to how quickly the 5G networks evolve and become cost effective. We may have to wait until the beginning of next decade for this dream to be realized. When governments promise to build smart cities, we need to be aware that it is a long path ahead.
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Mamidala Jagadesh Kumar is a Professor of Electrical Engineering at the Indian Institute of Technology, New Delhi, India. He is the Editor-in-Chief of IETE Technical Review and an Editor of IEEE Transactions on Electron Devices. He has widely published in the area of Micro/Nanoelectronics and is known for his excellence in Teaching. More details about Dr. Kumar can be found at http://web.iitd.ac.in/~mamidala