Significant challenges for seamless surfing

The latest improvements to mobile networks have allowed new services and created a new set of end-user expectations, witnessed by the rise of more complex and data-hungry applications for smartphones and tablets. Some applications now support ‘seamless connectivity’, or the ability to continue using an application when moving between devices without interruption to the content. Providing this capability requires access to and control of the content over multiple networks; WiFi, cellular and broadband. With mobile data consumption currently forecast to almost double year-on-year for the next five years, the network operators maintain they will struggle to meet long-term demand without more spectrum.

To support the huge increase in the numbers of devices and performance requirements, studies describe the key network attributes that will be required: an integrated wireline/wireless network, where the wireless part is a dense network of small cells with cell data rates of the order of 10GB/s made possible by high-order spatial multiplexing (MIMO). A round-trip latency of 1ms will give the ability to deliver the interactive high-resolution streaming video that’s needed for ‘immersive virtual reality’ applications. It’s now assumed that devices will support simultaneous use of multiple air interfaces, including not only extensions to today’s RF cellular frequency bands, but also operation at microwave or millimetre frequencies. With these attributes, the combined network will support everything from simple M2M devices to next-generation phones, tablets and PCs, with the monitoring and control of literally billions of sensors and multiple simultaneous streaming services, while supporting the massive data collection and distribution needs of the IoT.

The ‘everything everywhere and always connected’ vision for 2020 and beyond that’s presented in the studies for 5th gen networks assumes a number of new paradigms: devices can operate at frequencies from a few hundred megahertz to greater than 100GHz, indoor cell sizes that may be as small as a single room, and a dense network of pico- and femto-cells to maximise the number of users that can be supported. 5G’s goal is to provide a high-capacity network capable of 10Gb/s peak and always delivering 1Gb/s rate to however many users want it; in other words to provide each user with ‘infinite’ bandwidth; all the bandwidth they need, anywhere, anytime including crowded areas such as sporting events and conventions. None of the studies have specific details of the core network that joins everything together, but they all assume the seamless connectivity mentioned earlier is a given.

In the cellular world, capacity gains come essentially from three variables: more spectrum, better efficiency and better frequency re-use through progressively smaller cell sizes; all of these areas are being investigated. Researchers are looking at a wide range of frequencies from current cellular frequency bands to 28, 38-40, 57-64, 70-75, 81-89 and even 140GHz. They are looking at wide bandwidths from 0.5 to more than 3GHz and antenna research with multiple-antenna configurations to increase capacity and focus cell performance in the direction of specific devices. Work continues on small cells and heterogeneous networks, with new techniques for self-organising networks, software defined radios capable of multiple air interface standards and software defined networks based on cloud computing are already being proposed for future 4G standards releases, and these will be extended to 5G. And they are investigating new physical layers such as GFDM, FBMC, UFMC, BFDM and NOMA.

Challenges

The World Radio-communication Conference, hosted by the International Telecommunication Union, is held every three to four years. Its mandate is to agree international radio frequency issues, including frequency allocation standards for mobile networks. The next WRC is scheduled to be held in Geneva in 2015 (ITU-R WRC-15) where initial discussions of 5G will be held.

Compared to previous generations of mobile network, 5G presents a number of new design and test challenges. Component and system design and test at microwave and millimetre frequencies has been around for many years, but its application to high-volume, low-cost devices for the consumer market is relatively recent. There’s already an unlicensed frequency band being used at 60GHz for the wireless LAN standard 802.11ad, which features a 2GHz channel bandwidth. Similar use may be made of licensed spectrum in the 28GHz range, where Samsung and others have already reported experimental results, and in other ranges, where a number of university studies are under way.

Figure 1 - 60GHz stimulus/response test system with software

Work is underway on channel modelling, to characterise how signals behave at mmWave frequencies. In ‘real’ user devices, these frequencies would likely use antenna components bonded directly to the transmitter and receiver chips, making connection to test equipment a challenge. This type of configuration has inherent issues in providing reliable and repeatable system calibration. Base station radios will typically feature antenna matrices for beam steering (directing RF attributes towards a specific device) and/or multiple transmit/receive streams (MIMO) for capacity enhancement. Testing user devices will mean emulating these real-world network conditions and test equipment suppliers will need to provide new channel measurements and simulation models for initial development and complex baseband and microwave sources for performance verification. Figure 1 shows a system designed for testing 802.11ad components at 60GHz and gives an idea of what might be needed for millimetre wave 5G design and development.

Any potential new PHY attributes are still to be decided, but it’s likely that any 5G devices will need to operate in a number of different Radio Access Networks (RANs). The new PHY will include new modulation and coding schemes that are more efficient at very high symbol and bit rates (e.g. the use of Golay sequences in 802.11ad). Challenges here include everything from battery power consumption (meeting user expectations) to supporting receiver systems that can demodulate and decode data from multiple carriers using different PHY characteristics simultaneously, then integrate the data into a single useful data stream.

Today, research into next-gen systems is being carried out in universities, either on their own or as part of consortiums or forums with support and direction of commercial partners, or in the R&D departments of network equipment manufacturers, chip and device manufacturers and network operators. While the standardisation process for next-generation may not start until 2015, it’s expected that some of the research currently under way will be incorporated into the next-generation communications systems which will begin to roll out around 2020.

Blue sky thinking

With investigations being totally open to many areas, researchers need a wide range of solutions with much flexibility to cover all the frequency ranges and all the analysis needs. Today, Keysight provides full range of flexible simulation and measurement tools that bring insight to this research. Vector network analysers allow in-depth design and test of millimetre wave components up to 110GHz, such as the antenna array elements needed for beam-steering and MIMO. With anticipated devices from simple sensors designed for years of unattended use, to next-generation smartphones and tablets, battery life will be key to meeting user expectations. Keysight battery drain analysis systems offer designers a power management solution to test their devices under normal, high and low voltage conditions. For the physical layer, where advanced digital signal processing meets RF, SystemVue is a system-level design automation environment that accelerates design and verification of communications systems. It combines with Keysight measurement products to create an expandable environment for modelling, implementing, and validating next-generation communications systems. It enables a virtual system to be verified from the first day of a project, beginning with simulation models, and gradually incorporating more real-world measurements as the design is translated into working hardware. It can be used in conjunction with Keysight signal sources to create complex arbitrary waveforms to verify theoretical channel models once the design is implemented. SystemVue can also be used in conjunction with Keysight 89600 VSA software, a comprehensive set of tools for demodulation and vector signal analysis. VSA works with a range of measurement tools: benchtop and modular signal analysers, digital oscilloscopes and wideband digitisers, to match the frequency and bandwidth of the signal to be analysed. Together these measurement, simulation, and signal generation and analysis tools enable the exploration of virtually every facet of the components and signals that will become part of the advanced designs needed for next-gen communications systems.