This paper presents a detailed analysis of Wr@p technology (Web Ready Appliances Protocol, also known as Power Modulation), an ultra-low-cost powerline communication solution devoted to the electrical appliance market. Wr@p technology is aimed at adding communication capability to a household appliance without affecting its industrial cost, thus speeding up the diffusion of “smart” appliances interacting with the power distribution grid and contributing to the smart grid paradigm.
A Wr@p transceiver establishes a narrow-band powerline communication exploiting the “last meter”, i.e. the power supply cord between the appliance and the outlet, where a proxy device, the smart adapter (SA), flexibly deals with standard home networking solutions. At the appliance side, such an approach allows for (i) connectivity at negligible cost and, (ii) keeps hardware and software virtually independent from the actual home networking protocol (since different configurations of the smart adapter take care of it). In this work, after recalling the basics of Wr@p point-to-point communication, an extension to the multipoint-to-point scenario is introduced. Design of silicon implementations integrated into commercial microcontroller architectures are presented and the results of extensive test of fabricated devices under actual operating conditions are detailed. Moreover, we present a complete Wr@p development solution, featuring wireless networks integration.
Wr@p the last meter technology for energy aware networked smart appliances
1. Wr@p: the Last Meter Technology for
Energy-Aware Networked Smart Appliances
A. Ricci∗ , E. Smargiassi§ , D. Mancini¶ , I. De Munari∗ , V. Aisa and P. Ciampolini∗
∗ Dept. of Information Engineering, University of Parma, Parma, Italy. Email: andrea.ricci@unipr.it
§ Elite s.c.p.a., Fabriano (AN), Italy. Email: enrico.smargiassi@elitetech.it
¶ SPES s.c.p.a., Fabriano (AN), Italy. Email: davide.mancini@spesonline.com
Indesit Company S.p.A., Fabriano (AN), Italy. Email: valerio.aisa@indesit.com
Abstract—This paper presents a detailed analysis of Wr@p1 meters and the power distribution network through suitable
technology (Web Ready Appliances Protocol, former Power Mo- communication infrastructures. Unfortunately, there are still
dulation), an ultra-low-cost powerline communication solution objective problems relating to connectivity that hinder the
devoted to the electrical appliance market. Wr@p technology
is aimed at adding communication capability to a household rapid and wide spread of these innovative home products.
appliance without affecting its industrial cost, thus speeding up In the past, several network protocols have been proposed
the diffusion of “smart” appliances interacting with the power- for control and monitoring of the domestic environment (e.g.,
distribution grid and contributing to the smart grid paradigm. LON [1], Konnex [2], Ethernet [3], WiFi [4], ZigBee [5]-[7]);
A Wr@p transceiver establishes a narrow-band powerline com- however, expensive communication nodes, as a matter of fact,
munication exploiting the “last meter”, i.e. the power supply
cord between the appliance and the outlet, where a proxy can only be embedded into high-end household appliances,
device, the smart adapter (SA), flexibly deals with standard home which are capable of bearing their unavoidable cost increase,
networking solutions. At the appliance side, such an approach whereas “standard” communication technologies are precluded
allows for (i) connectivity at negligible cost and, (ii) keeps to mass production of middle-range and low-end “white
hardware and software virtually independent from the actual goods”. Moreover, market has not converged yet on a single,
home networking protocol (since different configurations of the
smart adapter take care of it). In this work, after recalling the common home-networking standard, which makes the protocol
basics of Wr@p point-to-point communication, an extension to selection a multifaceted issue, leaving the field open to new
the multipoint-to-point scenario is introduced. Design of silicon smart solutions. To overcome all these problems, an original
implementations integrated into commercial microcontroller ar- approach has been proposed in [8]-[13], based on a “proxy”
chitectures are presented and the results of extensive test of approach (Fig. 1): bidirectional narrow-band point-to-point
fabricated devices under actual operating conditions are detailed.
Moreover, we present a complete Wr@p development solution, communication (called Power Modulation or Wr@pTM ) is
featuring wireless networks integration. established on the power-supply wire, between each appliance
Index Terms—Powerline communication, smart appliance, mi- and its outlet. A general-purpose communication node (called
crocontroller peripheral, smart grid, smart plugs, ZigBee. Smart Adapter, SA) is located at the outlet and acts as a
bridge between the Wr@p communication and the actual home
I. I NTRODUCTION networking protocols. By this approach, several advantages
Nowadays, the constant growing demand for energy and the may be attained: (i) communication costs at the appliance
antithetical call for climate changes reduction are producing side are negligible (transmission is managed by the appliance
a strong convergence of scientific, industrial and political control core itself by means of on-board peripheral); (ii) the
interests towards the use of information and communication appliance hardware and software are virtually independent of
technologies (ICT) in order to support a structural transfor- the actual home networking protocol, which is allotted to the
mation of each phase of the energy cycle: from generation to external smart adapter; (iii) new generation of smart plugs and
transmission, from distribution to accumulation and, above all, smart sockets can be designed, which are able to talk directly
the smart consumption of energy. This virtuous link between to plugged household appliances and spread the collected
ICT and the world of energy is commonly identified with information to the grid; (iv) the in-line production testing of
the term Smart Grid, or even Internet of Energy, in order appliances can be improved and accelerated; (v) appliances can
to highlight a paradigm shift that leads to a global network be remotely assisted without adding any cost to the product.
that carries energy, information and control between highly In this paper, we report on Wr@p technology updates,
distributed and cooperating devices and systems. This process development tools as well as applications. The contributions of
of great transformation of the global energy system involves the paper are the following: (i) an extension of basic point-to-
the direct collaboration of household appliances, in particular point transmission concept to the multipoint-to-point scenario
white goods, which, to this purpose, are becoming “smart” and by means of medium-access-control (MAC) techniques; (ii) a
will be able to exchange information with both digital power description of silicon implementation of Wr@p communica-
tion circuitry into commercial 8-bit and 32-bit microcontroller
1 Wr@pTM is a trademark owned by Indesit Company SpA, Italy. architectures; (iii) the analysis of Wr@p protocol mapping
2. receiver transmitter transmitter receiver
LS1 I DA
zc1
D1 D2
zc2
Vs Vs
mod ZPM BPF ZDA
M1 M2
T1
shunt
m(t)
power supply
cord PM
Power meter SoC PM-enabled appliance PC peripheral
Smart Adapter (a) Digital Household Appliance (b)
Fig. 1. Wr@p communication system: (a) smart adapter, (b) digital household appliance.
on ZigBee interoperable application layer (i.e. Cluster Library short (few tens of microseconds) and precise perturbations
level). (about 12 V in amplitude), superimposed to the mains voltage
The paper is organized as follows. In Section II, Wr@p waveform. Data are encoded by modulating the positions, with
technology basics are recalled and multipoint-to-point commu- respect to the zero-crossing of supply sine waveform. Fig. 2
nication is introduced. Section III gives details about cirtuitry shows the smart adapter transmission section, where a digital
implementations, in the form of microcontroller peripherals device (e.g. the digital core of a power meter system-on-chip)
and smart plugs, whereas in Section IV we describes the controls current flowing through zener diodes (D1-D2) by
fusion of Wr@p communication with wireless networks. In means of a couple of MOSFETs (M1-M2) and a relay (LS1).
Section V we present our experimental results, based on At the appliance side, reception is based on an extremely
Wr@p development kit. Finally, in Section VI, we draw the cheap analog front end (i.e. a band pass filter plus a couple
main conclusions of the paper. of Schmitt-triggers) and a few configurable digital counters,
again embedded into PM peripheral. Information data have to
II. W R @ P N ETWORK AND P ROTOCOL be duplicated and encoded four times per period, in order to
Details of Power Modulation (PM) physical link can be ensure that at least one pulse will trigger the receiver. Data
found elsewhere [13]. Here, we just recall its basic prin- duplication within each sine wave semi period (one instance
ciples (see Fig. 1): the forward link (from the appliance per quarter) is used to cope with unknown nature (capacitive
to the smart outlet) is based on the on-off keying (OOK) or inductive) of the appliance load. Plug orientation does not
modulation of the instantaneous power consumption of the impact on decoding procedures thanks to the data replication
appliance, in a synchronized fashion respect to the mains over adjacent mains semi periods. Measurements demonstrate
cycles. The appliance should include a Power Modulation- that it is possible to transmit at least one nibble (i.e. 4
enabled microcontroller (i.e. a device which features a simple bits) during each mains cycle, without exceeding noise limits
PM peripheral, see Section III) and, at least, one inexpensive set by regional standardization committees (e.g., CENELEC
electric load (ZPM ) - any electric load of the appliance itself, in Europe) and preserving the proper functionality of the
for instance - controlled through a triac (T1). If a single bit appliance.
per period is transmitted, depending on the mains frequency, At the appliance side, the digital encoding and decod-
a throughput of either 50 or 60 bit/s can be achieved. This ing procedures have been embedded into a microcontroller
relatively slow communication perfectly matches the typical peripheral, in order to (i) keep costs at a minimum and
appliance data notification scenarios: both white goods status (ii) guarantee performance and repeatability of operations.
and faults monitoring, as well as statistical and diagnostic data Household appliance manufactures can embed Wr@p-enabled
communication actually require the transmission of few bytes. microcontrollers into their products free of charge, thanks to
At the receiving side, a simple power meter is needed, in order the recent Power Modulation technology liberalization2 .
to reveal incoming data. Each bit is decoded by measuring A. Data-Link Layer
the mean power absorbed by the appliance during each k-
Data-link layer relies on a packet-based communication.
th cycle and comparing it to an adaptive reference threshold
The Power Modulation frame format is composed of a header,
(i.e. the weighted average over the n previous cycles’ power
a payload and a footer checksum. The general PM frame
consumption). The decoding scheme is very robust and reliable
structure is formatted as illustrated in Fig. 2. Packet Header
if simple power consumption oversampling is used. On the
is 3-byte in length, and contains synchronization preamble, a
reverse link (from the smart outlet to the appliance), data
bits are encoded according to a pulse position modulation 2 Agreement between Indesit Company and Renesas Electronics signed on
(PPM) scheme. The smart adapter generates intentional, very March 29th, 2010
3. Octets
3 0 to 32 2
count ^I/2,I/4,..,I/32` Noise canceler PMVZ
Header Payload Footer I Noise canceler PMPZ
Prescaler
PMUGR
CRC-16
checksum
PMCR
Frame synch Command Length optional
Receiver Transmitter PMT
forward-link
Bus Interface
half bit
0xA5 : forward link (from DA to SA)
0x00 : reverse link (from SA to DA)
Fig. 2. Data-link layer frame structure. PMDR PMCDR
DDC/frequency Voltage Module
measurement measurement data bus
PMSR
Local serial bus
PMSR2
Interrupt
(a)
generator
Power Modulation Interface
Home Application Metering
network node processor circuitry
CPU Internal data bus
Other peripherals
(b)
Fig. 4. Power Modulation peripheral architecture, integrated in both 8-bit
Fig. 3. Multiple smart adapter (MSA) devices: (a) replicated metering H8/36079PMI and 32-bit RX210 microcontrollers.
circuitry; (b) PM channel sharing.
command identifier and payload length sub-fields. solution, Fig.3(a), requires several replicas of the metering
During forward link transmission, Frame synch byte is set circuitry, one for each connected appliance. The MSA embeds
to 0xA5, in order to enable smart adapter for power threshold only one standard home-networking node, which routes all
estimation (i.e. 0xA5 contains an equal number of high and the collected information coming from each PM channel
low bits). An optional high half-bit can be added at the end towards the residential network. Depending on the selected
of forward link frames, providing smart adapter with plug metering device some optimizations could also take place in
insertion information (i.e. transmission reference). the metering section: if advanced SoCs are selected (featuring
The reverse link exploits 0x00 as frame synchronization pat- digital programmable cores and multiple conversion channels)
tern; at the receiver side, the difference between nominal and only current detector replicas are actually required, in order to
actual pulse positions is computed and offset compensation is talk simultaneously with several digital appliances.
applied to the following frame data. The Command identifier When device cost and size reduction is the main MSA design
subfield specifies the packet class being used. Valid commands driver, some more savings can be attained, trading cost with
include appliance identification and arbitration (see II-B) as bandwidth. Following this second approach, all the available
well as white good control and monitoring classes. The sockets are connected in parallel (Fig.3(b)) and the Power
Length byte specifies the payload field byte count whereas Modulation channel is shared among white goods, according
the Checksum, based on standard CRC-16-CCITT generator to a TDMA policy, i.e. the available channel is divided,
polynomial, enables for communication error detection. A along the time dimension, between potential participants. The
simple stop-and-wait ARQ retransmission policy can be imple- procedure of collision avoidance is a SA-driven synchronous
mented, in order to reduce physical layer bit-error-rate (BER) mechanism, with all the appliances’ data transfer handled by
on both forward and reverse link. The experimental analysis, the smart adapter, by means of a singulation process. The
detailed in Section V, regardless of the operating conditions selected anticollision scheme is a conventional binary tree-
(i.e. static or time-varying loads), indicates a residual BER based algorithm (used, for example, in passive RFID systems)
figure well below 10−6 at the data-link layer, which is more and can be implemented inside the SA application microcon-
than adequate to the actual purpose. troller. In order to partecipate to the arbitration sessions, each
appliance requires an unique identifier (ID), either assigned
B. Multipoint-to-Point Communication during production phase (e.g. a subset of manufacturer codes)
Basic “single-access” smart adapter device (SSA) featuring or randomly generated. The appliance ID length can be limited
a point-to-point Power Modulation link can be extended to a to one byte, thanks to the reduced number of appliances which
multipoint-to-point scenario, i.e. several household appliances share the same medium (usually up to 5-10). The tree-based
talking with a multi-socket smart adapter (MSA) device. algorithm represents a two-way handshake process involving
This multiple “proxy” service can be implemented following sequences of interaction between the smart adapter and the
mainly two approaches, depicted in Fig.3. The straightforward appliances, known as the interrogation cycle. The objective
4. TABLE I
of these interrogation cycles is to split the appliances, using ATTRIBUTES OF THE W R @ P P ROTOCOL T UNNEL S ERVER C LUSTER .
their identifier, into reduced sets of devices. The splitting of
the IDs binary tree into two branches (leaves) is based on the ID Name Type Access Man./
Opt.
bit collisions. Obtaining collision information at the bit level 0x0000 SmartAdapterClass 8-bit Read-only M
can be revealed at the smart-adapter side observing deviations enumeration
from nominal appliance absorbed currents (estimated during 0x0001 DeviceActiveMask 16-bit bitmap Read-only M
0x0002 DeviceComMask 16-bit bitmap Read-only M
packet preambles). Through singulation process, the smart 0x0003 DeviceIDList Array of Read-only O
adapter collects the identifiers of plugged appliances. After this unsigned
discovery phase, SA can talk directly with each white good or 8-bit integer
it can assign each appliance a time slot for spontaneous data
TABLE II
notifications. C OMMANDS ID S FOR W R @ P P ROTOCOL T UNNEL S ERVER C LUSTER .
III. P OWER M ODULATION P ERIPHERAL I MPLEMENTATION Commands Received
In cooperation with Renesas Electronics Corporation, we Command identifier Description Man./Opt.
field value
investigated Wr@p technology implementation, based on the 0x00 Wr@p Frame Transmission M
integration of communication physical layer within commer- Request
cial microcontroller architectures as a dedicated peripheral 0x01-0xff Reserved -
(referred as Wr@p Interface or Power Modulation Interface, Commands Generated
Command identifier Description Man./Opt.
PMI) . The impact on silicon area of the microcontroller field value
would be almost negligible, and software code of PM data- 0x00 Wr@p Frame Transmission M
link layer would result extremely simple, thus leading to Response
0x01-0xff Reserved -
a cost- and performance-effective solution. Hence, we have
designed a digital architecture implementing the PM manage-
ment functionalities. VHDL language has been exploited to Octets
3 0 to 32 2
count
this purpose. The Power Modulation Interface (PMI) block Wr@p data-link
frame structure Header Payload Footer
diagram is reported in Fig. 4. The architecture includes both
CRC-16
communication modules and a mains line monitor block. The checksum
octets(2-34)
latter could be profitably exploited to enable demand-side Frame synch Command Length optional
forward-link
octet(1)
power management policies. As an example, measuring the octet(0)
half bit
mains voltage frequency the power-grid actual load status can
be inferred: adapting the user’s load to the grid health status, Frame Man. code Transaction Command
control sequence identifier
fluctuations. in the power requirement could be smoothed out, number
thus reducing the need for spinning reserves (i.e. on large
numbers, reducing greenhouse gas emissions) [14]. PMI is ZigBee ZCL-level
ZCL Header ZCL frame payload
frame structure
extremely flexible: more than ten 8-bit registers give access
to several peripheral configurations, enabling the adaption of e.g. Wr@p Frame
0x00 DeviceID Wr@p octets(0,1,..,34)
Transmission Cmd
communication capabilities to different scenarios. First, the
physical implementation of PMI (which requires less than 10 k
Fig. 5. Wr@p protocol mapping into ZigBee application layer (exploiting
equivalent gated) has been carried out on a FPGA device, and ZCL approach).
tested on Renesas E6000 development system [13], [15]. Then,
the peripheral soft-IP has been integrated into two Renesas
microcontroller architecture, both a 8-bit H8 Tiny and a 32- appliance networking are currently under discussion, based on
bit RX210 device. Energy@Home3 initiative [17]. Moreover, ZigBee have been
selected as the communication solution for several commercial
IV. W R @ P TO Z IG B EE M APPING
“smart plugs” devices.
As already stressed above, the smart adapter device em- The fusion of Wr@p protocol and ZigBee stack has been
beds a conventional communication node, in order to route performed at the application level, following ZCL (ZigBee
incoming Wr@p messages toward a home network. General- Cluster Library [6]) specifications, in order to preserve appli-
purpose modular adapters can be designed, sharing design cation profiles modularity. A specific tunneling cluster can be
and manufacturing costs on larger production volumes. Smart build, including both server and client on an endpoint to tunnel
adapter devices can then be personalized, simply adding the Wr@p messages in both directions.
preferred communication module and mapping Wr@p network
communication onto the selected protocol. 3 Energy@Home is a collaborative project between Electrolux, Enel, Indesit
Here, we detail Wr@p-to-ZigBee mapping, since home Company and Telecom Italia, aimed at developing a communication protocol
that enables provision of Value Added Services based upon information
automation [7] and smart energy [16] interoperable application exchange related to energy usage, energy consumption and energy tariffs in
profiles are already available and some extensions related to the Home Area Network (HAN).
5. TABLE III
Digital Appliance board with
E XPERIMENTAL E RROR B IT R ATE OF W R @ P P HYSICAL L AYER . Wr@p-enabled microcontroller Smart Adapter
Expansion:
Load BER H8-36079PMI C
AFE C section to home
network
Capacitive Filter 3.75E-6 with PM peripheral M1 M2 (e.g. ZigBee)
10W Lamp 4.52E-6
Electric Motor (light routine) 5.62E-6 D1 D2
Electric Motor (medium routine) 6.25E-6 AFE Power Meter
LS1
Electric Motor (heavy routine) 7.12E-5 SoC
The proposed server cluster contains the attributes shown
in Table I. The read-only SmartAdapterClass attribute
specifies the proxy category (i.e. single, multiple with
replicated power meters (MSA-P), multiple with arbitra-
tion (MSA-A)). When multiple power meters are available,
3.3 V
DeviceActiveMask and DeviceComMask bit masks rep- regulator
resent the active (i.e. consuming power) and Wr@p en-
abled devices, respectively. The array of unsigned integer
DeviceIDList contains appliances IDs retrieved either di-
rectly or during the last arbitration session. All the attributes
Appliance load
can be read using cross-cluster ZCL commands and automat-
ically notified supporting ZCL attribute reporting. The client
cluster has no attributes.
Table II lists both received and generated commands whereas Appliance power supply cord
Fig. 5 details the basic mapping strategy. The ZCL Payload (Power Modulation channel) To the mains
outlet
should be filled with target Wr@p-enabled appliance ID Digital Appliance Smart Adapter
(DeviceID), followed by the actual Wr@p frame content, i.e.
Command, Length and Payload. The client cluster receives Fig. 6. Wr@p first development kit, based on H8/36079PMI microcontroller
the cluster specific commands generated by the server and and wireless-enabled smart adapter.
viceversa.
Since the ZCL command payload length is limited to 35
bytes, the Wr@p tunnel cluster does not require ZigBee field test, exploiting Wr@p development kit. To this purpose, a
fragmentation support, even if over-the-air High Security mode set of static and time-variable appliance loads were connected
is used. to the powerline, to simulate the actual operating environment.
For single smart adapters, the proposed cluster could share its First, measurements were performed using a barely resistive
end-point with other services, such as Simple Metering cluster load, represented by a small lamp, always connected to the
[16], as well as Appliance Identification and Control clusters power supply cord at the appliance side. The same device
[17], creating an enhanced appliance-aware “smart plug”. A was also exploited to perform downstream communication,
similar approach can be used for multiple smart adapters, modulating the current flowing over the power supply cord.
where multiple end-points (one for each power meter) may Next, capacitive and time-dependent inductive loads were
be implemented on the same ZigBee device. Following the taken into account, by connecting actual household appliances
proposed ZCL-level tunneling approach (largely adopted in to the network. Capacitive behavior was obtained, as an
the ZigBee specifications), a Wr@p communication channel example, exploiting appliance power-supply filters, whereas
can be instantiated inside every ZigBee devices, in a Smart an inductive load was given by the washing-machine electrical
Energy/Home Automation compatible fashion. engine. Time-dependent behavior was induced by performing
several different cycles with a washing-machine. We collected
V. W R @ P D EVELOPMENT K IT AND F IELD T ESTS
statistical data during repeated communication sessions (3·107
The new microcontrollers, H8/36079PMI and RX210, have information bits for each load state). Table III resumes the
eventually been fabricated and the former has been integrated experimental error bit rate of physical layer, evaluated under
into the first Wr@p development kit, depicted in Fig. 6. the different operating environments. The analysis, regardless
The kit includes a prototypal generic appliance main board of the load conditions (static or time-varying loads) and
and a smart adapter. The development solution enables for thanks to simple error-correcting (ARQ) software procedures,
testing communication and line monitoring features under indicates a BER figure well below 10−6 at data-link layer,
actual operating conditions. After preliminary functional tests, which is more than adequate to the actual purpose. Moreover,
used to validate the communication principle and investigate depending on the microcontroller main clock frequency (2÷32
the microcontroller peripheral performance, an extensive set MHz), peripheral clock (after the prescaler) spans from 1 to
of experimental measurements was carried out in a thorough 1.875 MHz, enabling for a 0.005% minimum precision in the
6. detection of mains period. (Country Manager, Renesas Technology) and Mr. Massim-
iliano Mazzoni (OEM Sales Manager, IBG Italy) for wafer
VI. C ONCLUSIONS
fabrication and their wide support to this work.
In this paper, we presented Wr@p technology, a straight- A special thank to Mr. Andrea Merloni, President of Indesit
forward and extremely cheap powerline communication tech- Company SpA (WRAP SpA President during Wr@p technol-
nology devoted to household appliances networking. Wr@p ogy development) for his initiative to liberalize Wr@p tech-
approach overcomes all the obstacles experienced by white nology in cooperation with Renesas Electronics Corporation.
goods manufacturers when using “standard” communication
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