I have given a keynote speech at the IEEE MASSAP Workshop at ICC 2015 in London. The talk is on wireless massive and ultra-reliable communications, which are seen as two new modes that will be featured in 5G. There is, of course, a technical part in the talk, but there is also a part which argues why the research on wireless and communication theory is still vital. The slides can be found here:
In many scenarios, M2M communications involve a massive number of low-rate connections. A showcase application is smart metering, consisting of a massive number of devices, up to 30000 , where meters periodically report energy consumption to a remote server for control and billing purposes. Massive communications present a new operating mode, not originally considered in the cellular radio access and that us why M2M-reengineering of the cellular systems has been so much into the research focus. In such a setting, conventional assessment of the system based on the average throughput is not sufficient.
We have instead asked a different question. Let us assume that each message that comes to the sensor needs to be reported within the deadline TRI with guaranteed reliability of, say 99.99%. There is a large number N of potentially reporting devices. How many cellular resources need to be used for such reporting and how to arrange those resources? There are two things that prevent us from assigning deterministic resources for reporting. One is that the arrival of a message at the device is a random process. Another is that the transmission from the device has a random outcome – the packet may end up in error and it will need to be retransmitted. In summary, the amount of resources required by each device is random.
We present a solution to this problem in our paper recently accepted at IEEE Wireless Communications Letters:
 Corrales Madueno, G.; Stefanovic, C.; Popovski, P., “Reliable Reporting for Massive M2M Communications With Periodic Resource Pooling,” Wireless Communications Letters, IEEE , vol.3, no.4, pp.429,432, Aug. 2014
The key idea to combat the individual randomness associated with each device is to take advantage of the statistical regularity that arises due to the fact that the number of devices N is massive. We show how to allocate resources using this statistical regularity and still guarantee 99.99% to each individual sensor.
A condensed version of the letter is given below.
How to achieve reliability without sacrificing system efficiency?
In , we consider a system with a periodically occurring pool of resources that are reserved M2M communications and shared for uplink transmission by all M2M devices (see previous figure). The re-occurring period is selected such that if a report is transmitted successfully within the upcoming resource pool, then the reporting deadline is met.
The M2M resource pool is divided into two parts, denoted as the preallocated and common pool, which reoccur with period TRI, as depicted in previous figure. We assume that there are N reporting devices, and each device is preallocated an amount of RBs from the preallocated pool dimensioned to accommodate a single report and an indication if there are more reports, termed excess reports, from the same device to be transmittedwithin the same interval. The common pool is used to allocate resources for the excess reports, as well as all the retransmissions of the reports/packets that were erroneously received.
The question that arises is: How many periodically reporting devices can be supported with a desired reliability of report delivery (i.e., 99.99%), for a given number of resources reserved for M2M communications?
We note that, if each device has a deterministic number of packets to transmit in each resource pool and if there are no packet errors, then the problem is trivial, because a fixed number of resources can be preallocated periodically to each device. However, if the number of packets, accumulated between two reporting instances, is random and the probability of packet error is not zero, then the number of transmission resources required per device in each transmission period is random.
The derivation of the individual reporting reliability can be found in . Promising results have been shown in the context of LTE, where even with the lowest-order modulation only 9% of the system resources are required to serve 30K M2M devices with a reliability of 99.99% for a report size of 100 bytes. The proposed method can be applied to other systems, such as 802.11ah.
 Corrales Madueno, G.; Stefanovic, C.; Popovski, P., “Reliable Reporting for Massive M2M Communications With Periodic Resource Pooling,” Wireless Communications Letters, IEEE , vol.3, no.4, pp.429,432, Aug. 2014
(Also available in http://massm2m.lab.es.aau.dk/publications.php)
The need to deploy large number of wireless devices, such as electricity or water meters, is becoming a key challenge for any utility. Furthermore, such a deployment should be functional for more than a decade. Many cellular operators consider LTE to be the single long-term solution for wide area connectivity serving all types of wireless traffic. GSM/GPRS is a well-adopted technology and represents a valuable asset to build M2M infrastructure due to the good coverage, device maturity, and low cost. We recently submitted a paper in which we assess the potential of GSM to operate as a dedicated network for M2M communications. In order to enable M2M-dedicated operation in the near future, we reengineer the GSM/GPRS/EDGE protocol in a way that requires only minor software updates of the protocol stack. We propose different schemes to boost the number of M2M devices in the system without affecting the network stability. We show that GSM a single cell can support simultaneous low-data rate connections (e. g. to smart meters) in the order of 10^4 devices.
Ideally, a TDMA system should be able to allocate as many as possible devices as long as the quality of service is guaranteed. However, in practice, systems are typically not able to operate in this manner. GSM and GPRS are an example of a TDMA system limited by the protocol rather than the application requirements of the smart meters. Specifically, for smart metering, a payload below 1000 bytes is expected. Moreover, the traffic patters corresponds to device originated with periodical reporting in the range of 5 mins, 15 mins, 1 hour and 6 hours. These devices tolerate a delay up to the next scheduled transmission opportunity if the message was not successfully delivered.
The main idea is that resources are pre-allocated according the application needs. In this manner, thousands of simultaneous connections can take place in a single cell (a single frequency is considered). In addition, we analyze the probability of reports exceed the deadline. This probability is presented in the following figure, where it is noticeable that for the most demanding case when RI=1min, a single cell could provide service for up to 5 · 10^3 simultaneous connections with a reliability of 99.99%. This number rises to outstanding value of 5 · 10^4 simultaneous connections that are served with 99.99%, if the reporting interval is set to 15 min.
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  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 .
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 , 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.
M2M has been a notable topic in IEEE Globecom 2012, ranging from tutorials, industry fora and a dedicated workshop, featuring technical papers and a panel. Perhaps the most interesting discussions were circling around the question which of the wide area wireless technologies will prevail and transform itself into a dominant M2M solution.
2G (GSM/GPRS) is a very mature technology, long abandoned by the cutting-edge research in wireless communications, but the one that has won the trust of the end users due to its ubiquity, reliability, energy efficiency and low cost. Our groups will soon publish a paper where we show that GSM/GPRS, using only rather minor software updates of the protocol stack, can be converted into M2M-dedicated system, in which a single cell can support 10000 simultaneous low-data rate connections (e. g. to smart meters). But, although technologically possible, 2Gmay not survive as a dedicated M2M solution on a long run due to other factors. First, in many countries 2G is scheduled to be closed down and release the frequency. the plan is to refarm the spectrum for LTE. Second, even if 2G can keep the operating frequency, the operators will not be willing to maintain multiple technologies in their network, and in that case LTE is a clear winner.
But, if 2G can technologically support various M2M applications, perhaps it can re-emerge in another form. For example, operate on a single frequency, keeping a narrow band and being owned by a M2M service provider i. e. not necessarily by a company that is also a mobile LTE-based provider. A more radical thought could be to put 2G in a certain license-exempt spectrum and large M2M users (e. g. utilities) may have their own 2G cells; the license-exempt operation could be created in a way to facilitate interference management among 2G cells that have different owners and are in proximity where they can cause interference. How about porting 2G into a “cognitive M2M radio”, by re-engineering it through protocol (software) updates?
Another thing is the role of 3G. The M2M discussion is very often between 2G and 4G; however, Qualcomm presented their solution in which CDMA-based protocols are re-engineered to support different M2M requirements (latency, reduced access overhead, etc.). Considering the impact of Qualcomm, it is clear that 3G should also be considered in the M2M discussion.
Finally, an emerging technology in the M2M arena is the sub-GHz WiFi specified as IEEE 802.11ah, dedicated to sensor networks and smart metering, and scheduled for finalization in May 2015.
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  and .
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.
 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
 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
Two of our researchers (German and Nuno) are at the 3rd ETSI Workshop presenting a poster about our ongoing work in enhancing the capacity of GPRS and LTE in the Radio Access Network.
There are more than 220 participants attending the workshop.
German and Nuno will post a summary of the events in the workshop in the end of the day.
If you are around come and visit them in the poster section during the coffee breaks.
Our research group was represented at the 1-way workshop on M2M communications arranged by FTW in Vienna. The program can be found here:
Petar’s presentation was about “Communication protocols for mass M2M access” and the slides can be found here.
Note: Most of the information contained in this post can be found in our IEEE Article:
Proceedings of IEEE Internation Conference on Smart Grid Communications (SmartGridComm 2014). IEEE, 2014.. IEEE Communications Society, 2014.
Today we present the major M2M standard groups that have been investigating M2M communications requirements and issues, namely European Telecommunications Standardization Institute (ETSI), 3rd Generation Partnership Project (3GPP) and 802.16 Machine-to-Machine (M2M) Task Group.
|Standard||Specification Description||Specification Reference|
|3GPP||sA1- M2M study Report||3GPP TR 22.868|
|sA1- MTC service Requirements||3GPP TS 22.368|
|sA2 – system Improvements for MTC||3GPP TR 22.888|
|sA3 – M2M security Aspect for Remote Provisioning and subscription Change||3GPP TR 33.812|
|sA3 – security Aspect of MTC||3GPP TR 33.868|
|3GPP study on RAN Improvements for MTC||3GPP TR 37.868|
|3GPP study on GERAN Improvements for MTC||3GPP TR 43.868|
|IEEE 802.16 M2M Group||Technical Report on usage scenarios, requirements, and standards changes needed for supporting Machine to Machine (M2M) Communication||IEEE 802.16p-10/0005|
|M2M Evaluation Methodology Document||IEEE 802.16p-10/0014|
|ETSI||M2M service Requirements||ETSI TS 102 689|
|ETSI||Smart Metering Use Cases||ETSI TR 102 692|
23.888 – System Improvements for MTC
The scope of this Technical Report (TR) by 3GPP is the architectural enhancements to support a large number of Machine-Type-Communication (MTC) devices in the network and the enhancements to fulfill the MTC service requirements.
|Group Based Optimization||0 Solutions|
|MTC Devices communicating with one or more MTC Servers||3 Solutions|
|IP Addressing||10 Solutions|
|Small Data Transmission||3 Solutions|
|Low Mobility||4 Solutions|
|MTC Subscriptions||1 Solution|
|MTC Device Trigger||19 Solutions|
|Time Controlled||6 Solutions|
|MTC Monitoring||11 Solutions|
|Decoupling MTC Server from 3GPP Architecture||4 Solutions|
|Signaling Congestion Control||11 Solutions|
|MTC Identifiers||7 Solutions|
|Potential overload issues caused by Roaming MTC devices||6 Solutions|
|Low Power Consumption||0 Solutions|
The main issues identified in this document are Signaling Congestion Control, MTC Device Trigger and MTC Monitoring. While many solutions are proposed to IP Addressing, which is related to the lack of IP address in IPv4 and therefore it is considered as deprecated.
Signaling Congestion Control an overload is an urgent problem that Network Operators (NO) are currently facing. Though this issue can be partially solved in the application side to operate in a network friendly manner, it is difficult for network operators to influence the application developers.
MTC Device Trigger: many applications requires to remotely request reports from the MTC devices.
MTC Monitoring: For many MTC devices it is desired that the network detects and report events causes by those devices that may result from vandalism or theft of the communications module.
We also like to mention Group Based Optimization issue, which can help to alleviate the redundant signaling to avoid congestion. MTC devices can be grouped together for the control, management or charging facilities etc. to meet the need of the operators.
43.868 – GERAN Improvements for Machine-type Communications
The scope of the document compromises: GERAN enhancements for Smart Metering, improve efficient use of Radio Access Network (RAN) resources and overload and congestion control.
The current status of this TR is the definition of common assumptions for simulation tests, where M2M traffic models are provided for synchronous and asynchronous users. More precisely three traffic models are presented:
|T1||MTC devices accessing the network in an uncoordinated/non-synchronized manner|
|T2||MTC devices accessing the network in a coordinated/synchronized manner with a certain distribution|
|T3||Legacy devices accessing the network in an uncoordinated/non-synchronized manner|
37.868 Study on RAN Improvements for MTC
The study aims to study the traffic characteristics of different M2M applications and define new traffic models based on these findings. RAN enhancements to improve the support of MTC. These improvements are:
- Access class barring scheme
- Separate RACH resources for MTC
- Dynamic allocation of RACH resources
- MTC specific back off scheme
- Slotted access
- Pull based scheme.
Furthermore examples of RACH load for smart electric metering, fleet management and Earthquake monitoring are provided.
22.368 Service Requirements for MTC Communications
This document identifies the general requirements for MTC and where network improvements are needed to handle the specific nature of MTC communications.
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… Therefore the applications do not all have the same characteristics. The following MTC Features have been defined:
- Low Mobility
- Time Controlled
- Time Tolerant
- Small Data Transmissions
- Mobile Originated Only
- Infrequent Mobile Terminated
- MTC Monitoring
- Priority Alarm
- Secure Connection
- Location Specific Trigger
- Infrequent Transmission
- Group Based MTC Features
- Group Based Policing
- Group Based Addressing
IEEE 802.16’s Machine-to-Machine (M2M) Task Group is a relevant resource in terms of traffic characteristics and traffic models for Smart Grids and M2M applications.
|Application||Access Interval of Interest||Access Attempt/second
|Meter Reporting||5 minute||40||116.7|
|Meter Reporting||1 minute||200||583.3|
|Unsynchronized Alarm Reporting or Network Access||10 second||1200||3500|
|Last Gasp Event Reporting||500 millisecond||24000||70000|
To finish this post, the following two tables provides an excelent view of M2M Traffic patterns, where the average message size and the attempts per seconds is specified.
Current cellular mobile networks are designed for human communication, and therefore are optimized for the traffic characteristics of human-based communication applications, i.e. communication with a certain session length, data volume, interaction frequency and patterns.
As the number of Machine-to-Machine (M2M) type devices increases so does the motivation to optimize existing cellular networks. While the features of the traffic generated by M2M devices are varied and application specific, the connected devices will be a mix of sensors and actuators. It is expected that a large majority will be sensors; therefore a bulk of the generated traffic will be in the uplink direction, i.e. from the M2M devices towards the network.
According to a recent market research study, in the next 10 years it is expected that the amount of M2M devices connections will reach 2.1 billion and that from these 61% will be due to the utilities market .
There are two interesting points about the characteristics of the traffic generated by this kind of application: The first is that the amount of data reported is generated sporadically and in small amounts, i.e. only a few bytes at a time; The second is that due to the expected density of the devices and the observed correlation between the reporting times , then the network will often observe a traffic pattern similar to a botnet, i.e. the traffic will arrive in batches. These two points will have an adverse effect on current cellular networks.
Currently, if one of these M2M devices wants to send a report to the network it will most likely use as carrier a SMS message. For this to happen, first the device needs to be connected to the network, which entails significant signaling overhead , then there is also the overhead associated to the transmission of a SMS message. Therefore, in the case of batch arrivals this will easily lead to the network to become overloaded due to signaling, while only transmitting a limited amount of data.
The network overload can occur at the radio access network, i.e. from a multitude of devices towards a base station, where in this case the base station gets overloaded, or globally where several base stations convey the traffic to a core network node. The ultimate consequence is the induction of signaling congestion and high computational load in the network.
In future blog posts we will describe what are the ongoing efforts to optimize the cellular networks to handle the characteristics of this particular type of M2M traffic.
 2.1 billion M2M devices in 2021, http://www.analysysmason.com/About-Us/News/Press-releases1/M2M-forecast-2012-PR-Jun2012/
 M. Zubair Shafiq et al, “A First Look at Cellular Machine-to-Machine Traffic – Large Scale Measurement and Characterization” in Proceedings of the International Conference on Measurement and Modeling of Computer Systems (SIGMETRICS), London, United Kingdom, June 2012.
 Annex B.4 3GPP TR 37.868 V11.0.0