Ultra-Reliable Communication in 5G Wireless Systems

Wireless 5G systems will not only be “4G, but faster”. One of the novel features discussed in relation to 5G is Ultra-Reliable Communication (URC), an operation mode not present in today’s wireless systems. URC refers to provision of certain level of communication service almost 100 % of the time. Example URC applications include reliable cloud connectivity, critical connections for industrial automation and reliable wireless coordination among vehicles. This paper puts forward a systematic view on URC in 5G wireless systems. It starts by analyzing the fundamental mechanisms that constitute a wireless connection and concludes that one of the key steps towards enabling URC is revision of the methods for encoding control information (metadata) and data. It introduces the key concept of Reliable Service Composition, where a service is designed to adapt its requirements to the level of reliability that can be attained. The problem of URC is analyzed across two different dimensions. The first dimension is the type of URC problem that is defined based on the time frame used to measure the reliability of the packet transmission. Two types of URC problems are identified: long-term URC (URC-L) and short-term URC (URC-S). The second dimension is represented by the type of reliability impairment that can affect the communication reliability in a given scenario. The main objective of this initial work on URC is to create the context for defining and solving the new engineering problems posed by URC in 5G.

The full article is available here.


Initial systems concepts for 5G wireless: The METIS perspective

The METIS project has released a document describing initial system concepts for the 5G wireless system. Our research group is actively involved in multiple aspects of METIS and in this document I have participated in the capacity as a driver of the topic Ultra-Reliable Communication (URC). In addition to the common approach to work on detailed wireless technologies, METIS has also defined multiple overarching topics, termed Horizontal Topics, URC being one of them. A horizontal topic covers the system-level aspect of a certain new feature that is envisioned for 5G wireless systems and this document is an initial report on the system concept per horizontal topic. The document is available here and the executive summary is given below.


Executive Summary

The overall purpose of METIS is to develop a system concept that meets the requirements of the beyond-2020 connected information society and extend today’s wireless communication systems to support new usage scenarios. This is an immense task, residing at a level that is different from the level at which detailed technical innovations are created. Therefore, the task of overall METIS system concept has been segmented into system concepts related to five Horizontal Topics (HTs): (1) D2D – Direct Device-to-Device Communication, (2) MMC – Massive Machine Communication, (3) MN – Moving Networks, (4) UDN – Ultra-Dense Networks, and (5) URC – Ultra-Reliable Communication.

This document provides a first view on the system concepts associated with each HT and indicates the steps and directions towards integrating them into an overall METIS system concept in the remaining time frame of the project. Each HT creates a context for applying and optimizing the Technology Components (TeC) in the Work Packages (WPs). For example, Massive MIMO is a generic technology that can give rise to innovations applicable in UDN and supporting the performance requirements specified by URC. The five HTs are not independent and their interaction is the basis for creating the architecture that is capable to achieve the main objectives for METIS [MET13-D11]:

  • 1000 times higher mobile data volume per area,
  • 10 to 100 times higher typical user data rate,
  • 10 to 100 times higher number of connected devices,
  • 10 times longer battery life for low power devices,
  • 5 times reduced E2E latency.

These objectives have to be met at a similar cost and energy consumption as today’s networks. The research challenge is amplified by considering that the wireless scenarios in 2020 will feature communication modes and services that are not merely “more and faster of what we have today”. As an example, the vehicles of the future that are interconnected with very high reliability and low latency, improving the efficiency and safety on the road. The METIS system will respond to the requirements for improved: 1) efficiency in terms of energy, cost and resource utilisation than today’s system 2) versatility to support a significant diversity of requirements, e.g. connections in Gbps from few devices vs. connections in kbps from many machine-type devices, inclusion of moving networks vs. statically deployed sensors, etc. 3) scalability in terms of number of connected devices, densely deployed access points, spectrum, energy and cost.

The concepts presented in this document are clearly demonstrating the capability of the HTs to channelize the technical innovations towards creating the overall METIS system. The highlights for the system concepts of the individual HTs are given as follows:

  • The HT D2D concept addresses the utility of the local exchange of information among the devices and creates a framework for solving the associated technological challenges. Putting D2D connectivity as a basic architectural element in the 5G system, rather than having it as an add on to an already existing architecture, leads to multiple benefits: increased coverage (availability and reliability), offload backhaul (cost efficiency), provide a fall-back solution (reliability), improve spectrum usage (spectrum efficiency), typical user data rate and capacity per area (capacity density), and enable highly reliable, low-latency Vehicle-to-Infrastructure (V2X) connections. Efficient D2D operation critically depends on interference management, resource allocation, efficient relaying for coverage extension, etc.
  • The HT MMC concept contains the technologies for radio access that will be capable to support an unprecedented number of devices. They are segmented into three types of radio access: (1) direct access, which devices transmit directly to the access node; (2) access through accumulation/aggregation point; and (3) machine-type communication between devices. The TeCs used to support these types of access fall in several categories: overlay of multiple transmissions (by means of quasi-orthogonal random access, sparse coding, successive interference cancellation, and reuse of resource by short-range links), smart pre-allocation of resources (persistent scheduling), techniques to lower the sync requirements and context/service-aware configuration of the radio access.
  • The HT MN concept introduces innovative directions for the future relationship between vehicles and wireless communications. Three clusters are defined: (1) MN for mobility-robust high-data rate communication links (MN-M), to enable broadband as well as real-time services in mobile terminals and moving relays; (2) MN for nomadic network nodes (MN-N), to enable a flexible and demand-driven network deployment; (3) MN for V2X communications (MN-V), to enable reliable and low-latency services such as road safety and traffic efficiency. While the MN-M cluster represents an evolutionary improvement of the existent technology addressing highly mobile scenarios, the MN-N and MN-V clusters introduce a paradigm shift in the usage of mobile communications.
  • The HT UDN has defined a core specific concept optimized for the potential stand- alone operation of a layer of ultra-densely deployed small cells. Beside considerations on a new spectrum flexible air interface, it foresees a potentially tight collaboration of nodes w.r.t. resource allocation coordination, a fast (de-)activation of cells and inbuilt self-backhauling support. An extended UDN concept offers additional performance improvement by: 1) Context awareness for mobility, resource and network management, 2) inter-RAT/ inter-operator collaboration, 3) tight interaction of a UDN layer with a macro layer holding superior role in control and management functions over common area, and 4) macro-layer based wireless backhaul for flexible and low- cost UDN deployments.
  • The HT URC system concept targets operation modes that are not present in today’s systems. URC-L (Long-term URC) targets the following operation mode: when not possible to operate at the peak rate, provide reliable moderate rates to all users instead of failing some of them. URC-L will be instrumental for the cloud-based services of the future. URC-S (Short-term URC) aims to guarantee latency despite the competition from multiple users and varying channels and will be critical for e.g. V2X connectivity. URC-E (URC for Emergency) aims to provide minimal guaranteed connectivity upon infrastructure damage. A generic URC toolbox consists of: spectrum allocation and management, robust PHY mechanisms, signalling structure and interface management, Multi-RAT and reliable service composition.

Based on the current view on the system concept, METIS has selected two technology components for implementation test-beds. The technology components are “Direct network controlled device to device communication with interference cancellation” to be implemented on the Radio Resource Management test-bed, and “FBMC/OQAM new waveform” for the Digital Base-Band test-bed.

The HT-specific concepts will be integrated towards the overall METIS system, which will contain new air interfaces as well as the evolved versions of today’s systems. In order to deal with such a level of complexity and support the required reliability/scalability, the METIS system will feature Software-Defined Networking (SDN), Network Function Virtualization (NFV), and Self-Organizing Network (SON) technologies.

The next steps of the work on the METIS system concept in the project include: further integration of the specific HT concepts with the METIS architecture, further positioning of METIS technical goals by the evaluation criteria defined for 5G systems and establishment of a technology roadmap for the deployment of the METIS 5G system.

First impressions on the IEEE 802.11ah standard amendment

As highlighted in the previous blog post, there is a new emerging standard in the M2M arena based on the IEEE 802.11 standards family. This standard is being developed under the IEEE 802.11ah group, and aims to define the physical (PHY) and medium access control (MAC) layers that operate at radio frequencies below 1 GHz. One of the goals of this standard is to ensure that the transmission ranges up to 1 km and that the data rates per user are above 100 kbit/s.

The standard is currently being drafted, but some essential details about this new standard are already available, which we will highlight in this blog post. It is important to emphasize that although the IEEE 802.11ah standard will define operations below 1 GHz, it will not use the TV white space bands (54-698 MHz in the US), which are targeted instead by IEEE 802.11af.

The PHY transmission in IEEE 802.11ah is an OFDM based waveform consisting of a total of 64 tones/sub-carriers (including tones allocated as pilot, guard and DC), which are spaced by 31.25 kHz. The modulations supported include BPSK, QPSK and 16 to 256 QAM. It will support multi user MIMO and single user beam forming.

In [1] is stated that stations will support the reception of 1 MHz and 2 MHz PHY transmissions. The channelization (i.e. operating frequency) depends on the region. In Europe it will be within 863-868 MHz, allowing either five 1 MHz channels or two 2 MHz channels. While in the US the available band will be within 902-928 MHz, allowing either twenty-six 1MHz channels or thirteen 2MHz channels. In Japan, the available band is within 916.5-927.5 MHz, with eleven 1MHz channels. In China the available band will be within 755-787 MHz, with thirty-two 1 MHz channels. South Korea and Singapore also have specific channelizations that can be found in [1].

The MAC layer will include a power saving mechanism and an alternative approach to perform channel access, which will allow an access point to support thousands of stations, as required for M2M applications. The channel access also supports a mode of operation where only a restricted number of stations can transmit.

There are several use cases for this standard [2], which include:

  • Sensor Networks – where the IEEE 802.11ah is used as the communication medium for the transmission of short-burst data messages from sensors, which include smart metering;
  • Backhaul networks for sensors – where the IEEE 802.11ah can be used to create the backhaul of mesh networks created by IEEE 802.15.4 networks;
  • Extended Wi-Fi range for cellular traffic off-loading – where the IEEE 802.11ah can be used to off-load traffic from a cellular network. The caveat is that the performance should be at least comparable with the one from the cellular network;
  • M2M communications – Whereas current systems are optimized more for human-to-human (H2H) communications, IEEE 802.11ah standard will mainly consider sensing applications.
  • Rural communication – Wireless communication in rural areas has led to some effort that is also titled as bridging the digital divide. Large potential is given by sub 1 GHz due to the wider supported range.

In future blog posts, we will follow up with the standardization activities in IEEE 802.11ah.

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ETSI M2M Workshop 2012: Day 2 Sony Keynote Highlights

We would like to briefly summarize the keynote given by Sony Limited Europe about Low Cost LTE Devices. The objective of Sony regarding M2M is to integrate in most of their devices some sort of M2M communication technology in the near future. Moreover they want to use the same technology to cover all kind of devices from TVs, cameras, videogame consoles, etc. However this suppose a great challenge due to the wide range of requirements for each of the applications in terms of delay, power and data rates. The question made by the presenter was:

“Is there any technology that encompasses all the varying M2M requirements?”

Nowadays we have a large variety of wireless technologies that could be used such as, ZigBee WiFi, GPRS, LTE, etc.

According to Sony point of view the LTE should be the one. Without going into detail, the overall idea is to develop a LTE Low cost device (approx. 10$ per module) that could be easily integrated in most of the their products.  Sony is not alone in the field of Low cost LTE device, in fact there is a on-going study in 3GPP since September 2011.

How to decrease the cost of LTE?

The main approaches are:

  • Reduction of the bandwidth
  • Hardware simplification
  • Reduction of TX power
  • Reduction of the peak rate

A 59% of cost reduction is expected from these simplifications.

However, the chip development of such Low cost LTE will not take place in the short-term, but in the year 2017.

One of the questions made in regards to this presentation was about using GSM/GPRS technology, which is currently available. According to Sony point of view, GSM may disappear and therefore the longevity of the solutions cannot be guaranteed.

In another post we will try to cover the one million dollar question: which technology will be available ten years or more from the current cellular networks GSM/GPRS, 3G(UMTS) or LTE?

WiFi Wake-up Receiver

The best way to reduce energy consumption of wireless device is to turn it on only when necessary. This is easy to realize if the transmitter and receiver know the exact timing of their communications, that is, if a complete rendez-vous can be accomplished between them. But of course, this is not the case most of the time since the traffic pattern over communications network is bursty and unpredictable: the receiver does not know when the transmitter wants to send packets to it.

Then, the transmitter can somehow poke a sleeping receiver when it needs to communicate. This is called wake-up signaling, and a lot of studies have been (and are being) done for sensor networks where the energy-efficiency of devices is one of the most important requirements. In general, the wake-up signaling is done through secondary channel. Here, the primary channel is the channel for data transmission/reception which consumes relatively high amount of energy. On the other hand, the secondary channel is only for sending wake-up message, which is realized by very simple and low-power radio. When there is no communications demand, only secondary channel is active, and radio interface for primary channel is completely turned off. Since the secondary radio consumes little amount of energy, we can significantly reduce the energy consumed in an idle state. That is, the gap of energy consumption between primary and secondary channels is exploited for energy saving.

We have been applying the concept of wake-up signaling to reduce the energy wastefully consumed by WiFi routers in a research project funded by Japanese government. The active duration of WiFi routers is much shorter than the idle duration. For example, WiFi router at your home is automatically powered-on/off according to your communications demands. A very simple wake-up receiver, which operates with non-coherent on-off-keying (OOK) detection, is installed into WiFi router. The energy gap between WiFi and such a simple receiver is so large that we can have a huge gain in terms of energy saving. But, one problem was the need for WiFi station (e.g. your laptop or smatphone) to have an additional device to transmit a wake-up signal.

Our solution to this problem was to reuse WiFi transmitter already installed into WiFi station. The simple, OOK wake-up receiver at WiFi router is designed to be able to detect the length of WiFi frames observed over 2.4 GHz ISM band. The WiFi station embeds information (e.g. wake-up ID) into the length of transmitted WiFi frames (you can imagine Morse code where the length of WiFi frame corresponds to dot and dash). The wake-up receiver turns on WiFi router if the detected length matches with its registered ID. The detailed information on wake-up mechanisms and receiver can be found in [1] and [2].

Basically, we have realized information exchange between WiFi transmitter and a very simple, low-cost, and low-power receiver which has completely different physical layer from WiFi. The layering concept has been developed to offer communications capabilities between devices having a common communications protocols. We have shown that, in a particular setting and scenario, communications between devices implementing different protocols are possible and useful. We are now seeking for scenarios in M2M where this type of communications and device can be exploited.

[1] Y. Kondo, H. Yomo, S. Tang, M. Iwai, T. Tanaka, H. Tsusui, and S. Obana,” Energy-efficient WLAN with on-demand AP wake-up using IEEE 802.11 frame length modulation,” Elsevier Computer Communications, Vol. 35, Issue 14, pp. 1725–1735, August 2012.  http://www.sciencedirect.com/science/article/pii/S0140366412001478

[2] H. Yomo, Y. Kondo, N. Miyamoto, S. Tang, M. Iwai, and T. Ito, “Receiver Design for Realizing On-Demand WiFi Wake-up using WLAN Signals,” in Proc. of IEEE Globecom 2012, Dec. 2012. http://arxiv.org/abs/1209.6186

Dealing with Short Data Packets

Many M2M applications use short data packets, going down to even several bytes. If a system is designed or analyzed under the assumption that the packets are short, then at least two issues should be taken into account:

  1. The size of the overhead or metadata becomes comparable to the data size.
  2. Near-optimal coding methods rely on large block lengths, and cannot be used in this setting.

Large percentage of overhead

The issue of metadata is often overlooked when putting forward conceptual (academic?) study of protocols and transmission methods. This is often because it is assumed that the packet is sufficiently long, such that a few bytes of metadata will be just an insignificant fraction of the whole packet. But, in the light of this, let us look at an ALOHA protocol run by, say 4000 devices. Assume that each device has only one byte of information to send. The meatadata of the packet sent by a node needs to be at least

log2(4000)≈12 [bits]

i. e. at least 50% more metadata than data in order to be able to address all the devices. This example could be extreme, but the main point is that the ALOHA protocol will spend at least 60% of the time, used for successful transmission, to send overhead. If we add the inherent loss in efficiency due to random access (idles and collisions), then the overall efficiency becomes quite low.

Coding rate for short packets

Information theory has been very good in teaching us how to send a large amount of data. But the elegant asymptotic results are not applicable, or even not indicative, when the packet has a short length. Let us take an example. If the Signal-to-Noise Ratio (SNR) at which the signal is received is S and the signal bandwidth is W, then we often, almost automatically, state that the data rate of the transmission is:

R_S=W log2(1+S)   [bps]

which is questionable since this is the data rate achieved over a channel with additive Gaussian noise, then codebooks that have their samples also distributed with the Gaussian distribution and, finally, the length of the codeword is N that goes to infinity. In that case, R_S (sometimes called Shannon formula) tells what is the maximal rate at which the probability for packet error will be approximately 0. In order to have a proper theoretical framework for short packets, perhaps one should resort to the recent advances in the area of non-asymptotic information theory.

But, another thing that should be kept in mind is that the coding/modulation that will be used by a simple M2M device will be also simple, far from the optimal Gaussian codebooks. In that sense, it seems viable to work with finite modulation (BPSK, QPSK) which is arguably not generic, but may provide more usable results for the scenario at hand.

The Rise and the Research of Machine-to-Machine (M2M) Communication

This is a research blog dedicated the communication technologies that are related to Machine-to-Machine (M2M) communication. We will primarily provide information related to our research project MassM2M, but also analysis of the relevant literature, technology trends, and research ideas.

What is M2M?

Probably today you have used M2M communication if you paid by a credit card. The terminal (a machine) in the shop connects to a server (another machine) in order to approve the transaction. M2M is about communication between devices, objects, things, which is different from Human-to-Machine (H2M) (e. g. “Googling”) or Human-to-Human (H2H) (e. g. “Skyping”).

Techno-economical forecasts indicate that in the coming years M2M communication will become massive, connecting tens of billions devices. Wireless chips have grown in capability and power efficiency, while shrinking in size and cost. It becomes affordable to embed wireless chips in many diverse objects and make them “digitally visible”, similar to the way a person is digitally visible through Facebook.

M2M becomes massive also in terms of diversity across applications. Wireless M2M networks are instrumental to manage the complexity of tracking, fleet, and asset management. The industrial sector can widely apply M2M in monitoring and control of processes and equipment. Radio Frequency Identification (RFID) in the retail industry is an example where M2M enables real-time visibility of the individual items. The M2M showcase is the smart grid: the evolved power grid where a rich information flow is used to balance the electricity production (e. g. windmills), distribution, storage, and consumption (e. g. large industrial capacities).

M2M has a large transformational power to make the processes more efficient by saving time, costs, and energy. But the present optimism about M2M is also fueled by its promise for new business models and the large innovation potential. The companies that use M2M, such as the industrial sector, can introduce novel features in their products and deploy new, information-intensive services. The companies that provide M2M services, such as the telecom operators, see them as important alternatives to the flat-data-rate-like services.

Skeptics may question the upcoming M2M revolution, pointing, for example, that RFID has been around for years, but failing to become massive. This is true; but it was also true that the phrase “smart phone” had been around from 1992, while it lifted off with the iPhone in 2007. Recall that the mobile phone started with voice as a single application at its focus, only to become our assistant and chief entertainer. M2M communication has started slowly with a wide range of applications, so our expectations should be very high for the upcoming billion connected devices.

Research on M2M

M2M services are already up and running in the networks of many mobile operators. Furthermore, there is are very active standardization processes related to M2M in different bodies, such as ETSI or 3GPP. So, is there a need/space for carrying out fundamental research on M2M communication technologies?

Our answer is (clearly) yes. Specifically, there are two (expected or predicted?) features of M2M communication that allow one to pose new and interesting research questions:

  • The “Massive” feature: Technology predictions say that by 2020 there will be 50 billion connected wireless devices, spanning a wide application range: smart grid, metering, control/monitoring of homes and industry, e-health, etc. Wireless networks need a revolutionary reengineering to be able to embrace the massive number of devices. In many cases M2M traffic will feature short data packets, where the useful data is comparable in size to the signaling overhead used to send that packet. To- day the networks can efficiently carry large data from few devices; the problem is how to carry few bytes from a large set of devices (machines). In a nutshell, sending 100000 bytes from one device is very different form sending 1 byte from 100000 different devices; the latter will clearly consume much more resources for signalling/coordination.
    •    The requirement for dependability. M2M communication becomes vital for various control, monitoring, and industrial processes, where it is critical to keep the wireless link alive during 99.99+% of the time. This is in a stark contrast to many existing systems, such as WiFi, which works fine around 95% of the time, but offers zero data rate under harsh receiving conditions. Increased dependability means that the wireless link is available almost all the time and, under harsh conditions, it can scale down the data rate in order to maintain reliable connection.

Other M2M issues that pose interesting research questions are security and device management. They are only peripherally related to our research, but it has to be noted that they also essential for wide adoption of wireless M2M deployments.

Regarding our research approach, we have two different tracks. In one track we investigate protocols and algorithms for rather generic communication systems. An example is Frameless ALOHA, where we are exploring a new concept for massive random access. In the second track we adapt our research context to a particular system, such as LTE, see the article on Code-Expanded Access in LTE. Although it may seem far from the cutting-edge research, we are very interested in the GSM system. We believe that the GSM networks should not be put out of use, but rather to be re-engineered and dedicated to M2M traffic. Even the research on GSM can become fundamental if we understand the GSM protocols and structure as design constraints for new protocols and signalling schemes that should be built on top of it. Our initial activities related to dependable wireless communication have been chiefly related to the university spinoff Wisecan.