1st day at the ETSI M2M 2012 workshop impressions

The talks on the first day of the 3rd ETSI M2M workshop were interesting. Along the day there were four thematic speaker sessions. The program is available here.

The first thematic session was dedicated to the ETSI current standardization efforts, where the main highlights was the recently started initiative OneM2M partnership project (http://www.onem2m.org/), which the mission statement is:

“The purpose and goal of oneM2M is to develop technical specifications which address the need for a common M2M Service Layer that can be readily embedded within various hardware and software, and relied upon to connect the myriad of devices in the field with M2M application servers worldwide.”

The speaker and ETSI board member Joachim Koss emphasized that the current M2M ETSI standard will be an important part in the upcoming oneM2M standard. The first release of the oneM2M standard is expected to come within one year time.

The second thematic session was dedicated to the ETSI M2M standard and included talks from industry. The focus was put on the current ETSI M2M architecture, what are the contributions of ETSI for M2M security standards, how should the device abstraction and semantics be performed. From these talks, it was interesting to see how the classification of security threats is currently being done (Check the slides when they become available).

The third thematic session was dedicated to the experience that several companies had when implementing the ETSI M2M standard in their products. From this talk it was highlighted that when in M2M the term constrained device is mentioned, it means different things to different people and therefore a holistic characterization should be considered. There was also some discussion about if the gateways are still required when IP become native in all devices, where the conclusion that it is still required but not for protocol translation.

The fourth and last thematic session was dedicated to the M2M in the industry. The talks included the efforts to align the smart metering industry approach with standards requirements and national security demands. The talk about smart grid was focused on how to leverage security and privacy. Finally the last talk was about road traffic assistance and the challenges that need to be addressed in 3GPP networks to be able to meet the requirements. One interesting example of the road assistance is to inform the driver what should be their average speed so that they are able to get in the green wave (i.e., catch green semaphores in a long stretch of the road).

The organizers will release the slides to the public at the end of the event.

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

MASS M2M at 3rd ETSI Workshop

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.

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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.

Distributed control of DGs within microgrid

In this blog we continue our overview on the use of M2M communications in microgrids (see https://massm2m.wordpress.com/2012/09/11/m2m-communications-in-microgrids/).

As outlined in the previous blog, the future smartgrid is envisioned as a network of microgrids. Microgrid is a small-scale electrical network consisting of localized distributed generators, storage capacities and loads, interconnected by low-voltage (LV) cables.

Distributed generators (DGs) within microgrid typically exploit renewable energy sources (such are photo-voltaic and wind generators) whose behavior cannot be controlled, posing new challenges with respect to balancing the generated power and user loads. Basically, when controlling the DGs within microgrid, the imperative is that their output voltages and frequencies should match.

In traditional grids, the voltage and frequency outputs of generators are regulated using the so-called droop control. Droop-control is essentially a proportional control algorithm that is executed locally at each generator, driving output voltage and frequency based on the locally measured active and reactive powers. Loads and generators in traditional grids are interconnected using high-voltage cables, which have much greater reactance then resistance. Taking into account this fact, it can be shown that, when the active and reactive power that are flowing into the cable from the generator are expressed through the generator’s voltage (and assuming that the power angle is small), the active power depends on the generator’s frequency and the reactive power depends on the generator’s voltage. The overall result is that, in traditional droop control, the frequency is regulated by the local measurements of the active power, and voltage is regulated by the measurements of the reactive power.

Traditional droop control cannot be used directly in AC microgrids[*], as resistance of LV cables dominates over reactance. One way to address this issue is to modify the droop control such that control algorithm includes the information exchanged among DGs[**] using communication network.

In a recent paper [1], the authors apply the paradigm of distributed consensus algorithms, exploited in their earlier works (see previous blog, https://massm2m.wordpress.com/2012/09/11/m2m-communications-in-microgrids/), to conduct series of local exchanges among DGs, in order for all DGs to learn what is the global state of active and reactive power. Traditional droop control is then augmented to include this information, such that frequency controller includes a term proportional to the differences between the desired and the actual active and reactive power, and the voltage controller uses a corresponding integral term. Using small signal analysis, the authors show that improved stability of the microgrid is achieved with respect to the traditional drop control.

The authors of [2] consider a similar setting, but the focus of their work is the impact of communication impairments, such are packet loss and delay, on the (modified) droop control, rather than on the control algorithm itself. The key observation is that outdated information about remote measurements, when combined with locally obtained measurements, can adversely affect the performance of the droop control. In order to neutralize this effect, the authors suggest a scheme in which locally obtained signal is delayed using the same delay distribution of the remote signal. The local delay is realized using Smith predictor and it is statistically the same as the delay of the remote signal. Finally, the authors present the simulation results obtained in an example microgrid with two DGs, showing that in the proposed scheme a more stable active power output is achieved, compared to the case when there is no local delay.

Recently, our group started collaboration on the same topic with a group at Department of Energy Technology at our university, with an aim of designing of robust and simple communication algorithms in the framework of DG control, both in AC and DC microgrids. The initial results are encouraging, however, we leave their presentation for our future blogs.

[1] H. Liang et al, “Decentralized Inverter Control in Microgrids Based on Power Sharing Information through Wireless Communications”, to be presented at IEEE GLOBECOM 2012

[2] S. Ci et al, “Impact of Wireless Communication Delay on Load Sharing Among Distributed Generation Systems Through Smart Microgrids”, IEEE Wireless Communications, June 2012

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[*] Regulation of DGs in DC microgrids will be addressed in our future blogs.

[**] Droop control is actually applied at inverters that connect DGs to the interconnecting AC bus.

M2M workshop at FTW in Vienna, September 26, 2012

Our research group was represented at the 1-way workshop on M2M communications arranged by FTW in Vienna. The program can be found here:

http://www.ftw.at/news/m2m-workshop-at-ftw-discusses-future-challenges

Petar’s presentation was about “Communication protocols for mass M2M access” and the slides can be found here.