M2M solutions for smart grid applications

In the emerging area of M2M communications, Automatic Meter Reading (AMR) is a showcase application: a large number of meters use sophisticated wireless networking for two-way communication with a central controller/data collector. The same holds for other smart grid applications, such as Automated Demand Response (ADR), substation and distributed energy resources automation/monitoring/control, and Wide Area Measurement System (WAMS), which all could be categorized within M2M communications.

The usage of wireless techniques for M2M communication has been made possible due to the level of maturity attained by the wireless technologies: small, inexpensive embedded devices have significant computational power and operate at very low power levels. M2M communication has significantly different requirements from, e. g. human -centric services (download, web browsing, video streaming), where large data volumes are sent and high data rate is required. In majority of the scenarios, M2M communication is based on intermittent transmission/reception of small data portions and pose requirements that are different from the ones according to which the common wireless protocols are designed. Some of the most important requirements are the following:
• Transmission from a massive number of devices and maintenance of a large number of active connections;
• Ability to send a small amount of data while decreasing the overhead percentage;
• Real-time communication with low latency;
• Certain connections that carry critical control data require a high degree of reliability, such that a connection should be kept alive more than 99.XX % of the time.
These requirements become more challenging when one considers the forecasts that state that by 2020 there will be 50 billion M2M connected wireless devices [1], spanning a wide application range: smart grid, smart metering, control/ monitoring of homes and industry, e-health, etc. While there are many ongoing standardization activities [2], M2M communication solutions have started to be deployed through the existing cellular interfaces, such as GSM and LTE; in fact, cellular networks are and will continue to be short to medium term enablers for M2M applications, due to their ubiquitous coverage and well understood and developed business/engineering platforms [3].

Indeed, in the past few years it has been observed an increase in the number of networked machines connected to cellular networks, like deployment of cellular-based wireless smart meters [4]. Some of those deployments are very large, such as Hydro- Quebec in Canada [5], with about 3.8 million devices that periodically send only a few bytes (KW/h consumption for instance). Another example is happening in Spain and Portugal, where Endesa, the largest Iberian operator, will replace a total of 13 million electric meters with smart meters by 2018 [6]. Since neither GSM nor LTE are originally designed to support massive M2M communication, there are ongoing research and standardization activities to modify those interfaces, notably LTE, in order to support the M2M traffic characteristics [7].

The adequate provision of M2M applications brings many challenges to cellular networks; the foremost being the support of the massive simultaneous transmission of low data rate messages. This led 3GPP to initiate a study item that concluded with the proposal of several key adaptations to the 3GPP cellular networks architecture, which will allow to both handle M2M traffic, denoted as Machine-Type Communications (MTC) within 3GPP [8], [9], and reduce the impact on human centric communications. The foreseen changes in order to support M2M traffic should happen both in the access and core network, and alleviate the radio and signaling network congestions that could lead to large delays, packet loss and, in the extreme case, service unavailability. Of particular interest are enhanced load control mechanisms in the radio access network, which include: access class barring [10], [11]; orthogonal resources [12]; dynamic resources allocation [13]; back-off; slotted access; pull-based.

Another recent standardization activity, spurred foremost by M2M applications, is within the scope of IEEE, where 802.11ah task group is developing a WLAN standard tailored for Wi-Fi-enabled devices to get guaranteed access for short and massive data transmissions [14]. The standard is still in its preliminary stages and it’s future operation is centering on the following principles: operating frequencies below 1GHz, BPSK, QPSK modulations and 16/256 QAM, while channel access should be group based, supporting up to 6000 devices simultaneously.

Finally, a potential, light weight solution for gathering of smart metering data is usage of Wireless M Bus technology [15]. However, this standard essentially foresees only uplink transmissions of metered data and lacks feedback control link, as well as capabilities of autonomous and adaptable operation in changing networking scenarios.

[1] Q. D. Vo, J. P. Choi, H. M. Chang, and W. C. Lee, “Green perspective cognitive radio-based m2m communications for smart meters,” in Information and Communication Technology Convergence (ICTC), 2010 International Conference on. IEEE, 2010, pp. 382–383.
[2] L. X. D. Niyato and P. Wang, “Machine-to-machine communications for home energy management system in smart grid,” IEEE Communications Magazine, vol. 49, no. 4, pp. 53–59, 2011.
[3] David Boswarthick, Omar Elloumi, Olivier Hersent, Eds,“M2M Communications: A Systems Approach”, Wiley, 2012.
[4] Sierra Wireless Product Webpage., Accessed in October 2012, http://www.sierrawireless.com/en/Solutions/customer stories/EDMI.aspx.
[5] Quebec Press Release Smart Metering., Accessed in December 2012, http://www.rogers.com/web/link/showNewsDetail?fromWhere=linkInRSSXml&rssBusiUnit=W&NewsID=1906177072.
[6] Endesa Press Release Smart Metering., Accessed in January 2012, http://www.endesasmartgrid.com/index.php/en/smart-homes/smartmetering.
[7] 3GPP, “Service Requirements for Machine-Type Communications (Stage 1),” 3rd Generation Partnership Project (3GPP), TS 22.368, June 2010. [Online]. Available: http://www.3gpp.org/ftp/Specs/html-info/23368.htm
[8] 3GPP TR 37.868 V11.0, Study on RAN Improvements for Machine-type Communications, October 2011.
[9] M.-Y. Cheng, G.-Y. Lin, H.-Y. Wei, and A.-C. Hsu, “Overload control for machine-type-communications in lte-advanced system,” IEEE Communications Magazine, vol. 50, pp. 38 –45, June 2012.
[10] S.-Y. Lien, T.-H. Liau, C.-Y. Kao, and K.-C. Chen, “Cooperative access class barring for machine-to-machine communications,” IEEE Transactions on Wireless Communications, vol. 11, January 2012.
[11] J.-P. Cheng, C. han Lee, and T.-M. Lin, “Prioritized random access with dynamic access barring for ran overload in 3gpp lte-a networks,”in GLOBECOM Workshops, 2011 IEEE, pp. 368 –372, December 2011.
[12] K.-D. Lee, S. Kim, and B. Yi, “Throughput comparison of random access methods for m2m service over lte networks,” in GLOBECOM Workshops, 2011 IEEE, pp. 373 –377, December 2011.
[13] M. J. Anthony Lo, Yee Wei Law and M. Kucharzak, “Enhanced lte advanced random-access mechanism for massive machine-to-machine (m2m) communications,” in 27th World Wireless Research Forum (WWRF) Meeting, 2011.
[14] S. Aust, R. V. Prasad, and I. G. M. M. Niemegeers, “IEEE 802.11ah: Advantages in standards and further challenges for sub 1 GHz Wi-Fi”, In 2012 IEEE International Conference on Communications ICC, December 2012
[15] EN 13757, “Communication systems for meters and remote reading of meters.” Part 4: Wireless meter readout (Radio meter reading for operation in the 868 MHz to 870 MHz SRD band), 2005.



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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M2M @ IEEE Globecom 2012

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.