ISO/IEC 14543-3-11:2016 情報技術—家庭用電子システム（HES）アーキテクチャ—パート3-11：エネルギーハーベスティング用に最適化された周波数変調ワイヤレスショートパケット（FMWSP）プロトコル—アーキテクチャと下位層プロトコル | ページ 6

3.1 用語と定義

このドキュメントでは、次の用語と定義が適用されます。

5.1 一般的なプロトコルの説明

5.1.1 概要

この節では、Frequency Modulated Wireless Short-Packet (FMWSP) プロトコル スタックの包括的な概要を説明します (表 1 を参照) FMWSP は、エネルギー需要と伝送衝突の可能性の両方を最小限に抑えるように設計された軽量のレイヤード プロトコルです。 FMWSP プロトコル スタックは、OSI 参照モデルの構造に対応しています (ISO/IEC 7498-1 を参照)

5.1.2 物理層

物理層では、データは 868.3 MHz, 902.875 MHz, または 928.35 MHz の周波数帯域で、周波数シフト キーイング (FSK) を使用して 125 kbit/s のデータ レートで送信されます。これは、国内規制の対象となる場合があります。 1 ビット期間は 8 µs です。データはパケットで送信されます。パケットは、プリアンブル (PRE)、同期ワード (SYNCWD)、それに続くデータ メッセージの長さ (LENGTH) と実際のデータ (DATA_PL) を表すバイトで構成されます。

プロトコルはプレシオクロナスで動作しています。プレシオクロナス システムでは、システムのさまざまな部分がほぼ同期していますが、完全ではありません。最大パケット長の制限内では、システムはメソクロナス (クロックの周波数は同じですが位相が異なる) と見なすことができます。同期ワード (SYNCWD) に基づく同期の後、システムは同期していると見なされます。これにより、非常にエネルギー効率の高いコーディング、つまりノンリターンツーゼロ（NRZ）コーディングを使用できます。

詳細については、第 6 条を参照してください。

7.1 概要

リンク層で送信されるデータの構造であるテレグラムには、2 つの異なる形式があります。 1 つは、長さが 8 B 未満の非常に短いテレグラム用です (7.2 を参照)他のテレグラムの長さは 8 B ～ 256 B です (7.3 を参照)データ リンク層は、データ整合性サービスも担当します。これについては、以下の 7.4 で説明します。

3 Terms, definitions and abbreviations

3.2 Abbreviations

4 Conformance

The three components of the FMWSP protocol system specified in this standard are the transmitter, the receiver and the repeaters. The repeaters shall be able to both transmit and receive telegrams and shall thus support the requirements for both the transmitters and receivers.

To conform to this International Standard the components shall support at least one of the three wireless frequencies 868,300 MHz, 902,875 MHz or 928,350 MHz unless another frequency is mandated by local regulations. For the frequency chosen, the transmitter shall support all the transmitter requirements that are not explicitly listed as optional, and the receiver shall support all the receiver requirements that are not explicitly listed as optional. These requirements are specified in Clauses 6, 7 and 8. The repeater shall, in addition to the requirements for a transmitter and for a receiver, also support the specifications in 8.3.

5 Architecture

5.1.3 Data link layer

A telegram is the part of a packet from which the preamble (PRE) and the synchronisation word (SYNCWD) have been removed. At the receiving end the telegram is transferred to the data link layer where the data integrity of the telegram is checked. If the data integrity check fails, the telegram is discarded.

5.1.4 Network layer

The network layer is responsible for routing, in this case primarily a repeating process, which is needed when the sender and recipient cannot communicate directly. This requires the existence of installed repeaters between them (see 8.3).

Another task of the network layer is to manage the timing of the received/transmitted telegrams. When possible, a listen-before-talk (LBT) technique is used to ensure that no transmission is initiated when the wireless channel is occupied.

5.1.5 Transport layer

This layer is not described in this standard.

5.1.6 Session layer

This layer is not described in this standard.

5.1.7 Presentation layer

This layer is not described in this standard.

5.1.8 Application layer

This layer is not described in this standard.

5.2 Data unit description

The communication protocol is based on units of data. The structure of the data units for each layer is described in Clause 6 (Physical layer), Clause 7 (Data link layer), and Clause 8 (Network layer).

A packet is the representation of the encoded data on the physical layer. It includes control and synchronisation information for the receiver. A packet is transmitted as a bit by bit serial sequence. At the receiving end, a telegram is the result of a decoding process, in which the fields preamble (PRE) and synchronisation word (SYNCWD) have been removed from the packet. At the transmitter side a packet is constructed by adding these two fields to the telegram.

6 Layer 1 – Physical layer

6.1 Overview

The physical parameters that shall be supported by the FMWSP protocol are described in this clause. The next subclause defines and illustrates the physical parameters that are specified in this standard. The requirements that a FMWSP transmitter shall fulfil are described in 6.3 and those for a FMWSP receiver in 6.4.

The physical layer is also responsible for the transformation between the transmitted data units in the physical layer, packets, and the transmitted data units in the link layer, telegrams. The structure and encoding of the FMWSP protocol packets are found in 6.5.

6.2 General description

This subclause describes the physical parameters for the FMWSP protocol, which shall be supported by the WSP signalling system. This includes all electrical parameters and associated tolerances for the transmitter and the receiver.

Centre frequency is the mean frequency between the mark frequency and space frequency of the transmitter (see Figure 1).

Data rate error specifies the difference between the actual data rate and the specified data rate divided by the specified data rate. The shorter the telegram the larger the allowed data rate error.

Data rate is the number of bits per second.

Frequency deviation (FDEV) is half the magnitude between the mark frequency and the space frequency. It has a maximum and a minimum value between which the peaks of the symbols have to lie (see Figure 1).

Frequency error is the difference between the centre frequency and the operating frequency (see Figure 1). It is positive when the centre frequency is larger than the operating frequency and negative when the centre frequency is smaller than the operating frequency.

Frequency modulation is done such that a logical 1 and logical 0 are represented by the mark frequency and the space frequency, respectively (see Figure 1).

Mark frequency is representing the logical 1 and has the value of the centre frequency added by the frequency deviation (see Figure 1).

Maximum tolerated signal is the maximum input level power a receiver shall be able to cope with.

Operating frequency is the frequency claimed by the system specification (see Figure 1).

Optimum sampling points are in the middle of the transmitted bit (see Figure 1).

Out of band spurious emissions are the frequencies not deliberately created by the system and these shall conform to the local regulations.

Packet Error Rate is the average fraction of transmitted packets that has not been correctly received, where each packet contains arbitrary data.

PA Ramp Off-Time is the time between the end of the last symbol of the packet and the time the transmitter is powered down (see Figure 1).

PA Ramp On-Time is the time between the transmitter has been powered on and the start of the first symbol of the preamble (PRE) (see Figure 1).

Pulse shape is the shape of the symbol. It can have an arbitrary form, but shall have its peaks located between the maximum and minimum frequency deviation values (see Figure 1).

Radio Frequency (RF) power is the strength of the transmitter measured at the antenna connector, if present. It should be made with equipment that has either been matched to the impedance of the antenna connector or corrected for any mismatch. For devices without an antenna connector, the measurements shall be interpreted as effective isotropic radiated power (EIRP) (i.e. a 0 dBi gain antenna), and any radiated measurements shall be corrected to compensate gain in the implementation.

Rated transmission power is the transmission power specified for the transmitter.

Receiver sensitivity is the minimum input power level for which the specified packet error rate under the conditions specified in 6.4 has been fulfilled.

Space frequency is representing the logical 0 and has the value of the centre frequency subtracted by the frequency deviation (see Figure 1).

Symbol is the bit transmitted by the sender representing either a logical 0 or a logical 1.

Transmission power is the power of the emission during transmission (see Figure 1).

6.3 Physical specifications for a FMWSP transmitter

This subclause provides the requirements for a FMWSP transmitter. Table 2 lists all required parameter values that shall be supported for both a transmitter and a repeater. These parameters have all been described in 6.2 above.

6.4 Physical specifications for a FMWSP receiver

This subclause provides the requirements for a FMWSP receiver. A FMWSP receiver shall be able to cope with the transmitted signals within the tolerances given in 6.3. It shall also fulfil the requirements in Table 3. These parameters have all been described in 6.2 above.

6.5 Packet structure

This subclause specifies the structure of a packet, i.e. the telegram as transmitted in the physical layer. Details for various aspects of the data encoding in the packet are described. The mode of transmission is with the most significant bit (MSB) first. The maximum length of a packet is 260 B.

The complete packet consists of the preamble (PRE), the synchronisation word (SYNCWD), the length (LENGTH) of the field DATA_PL followed by the payload DATA_PL as illustrated in

Figure 2 above and described in Table 4.

Every packet starts with the preamble (PRE) of length 16 bit (see Table 4).

PRE: This field, the preamble of length 2 B, is the start of packet and is used for threshold generation and bit synchronisation. Its value is seen in Table 4.

SYNCWD: This field is the synchronisation word, of length 2 B, serves to identify the FMWSP protocol and also used to synchronize the receiver to the incoming signal. Its value is seen in Table 4.

LENGTH: This field, of length 1 B, specifies the remaining number of bytes of the packet, which coincides with the length of the field DATA_PL.

DATA_PL: This field contains the payload data of the physical layer and will be described in detail in Clause 7. Its number of bytes is determined by the field LENGTH.

The relationship between a packet in the physical layer and a telegram in the link layer is described in 6.6.

6.6 Relationship between a packet and a telegram

A receiver needs to deduce the telegram from the packet, whereas a transmitter needs to create a packet out of a telegram. The relationship between them is seen in

Figure 3.

7 Layer 2 – Data link layer

7.2 Structure of a telegram of length less than 8 B

A telegram of a length less than 8 B is a telegram in which the value of the field LENGTH is less than or equal to 6 B. Its structure is shown in

Figure 4.

LENGTH: This field specifies not only the number of bytes following this field in the telegram, but also the type of the telegram as shown in Table 5. The length of this field is 1 B.

ORIGID: This field specifies the identity of the source of the telegram. The length of the field depends on the telegram type as seen in Table 5.

DATA_DL: This field contains the payload of the telegram. The length of the field depends on the telegram type a seen in Table 5.

Since there is neither any information about either repetition (see 8.3) nor for data integrity (see 7.4), these types of telegrams shall never be repeated. Also the upper layers are responsible for data integrity.

The semantics of a telegram type is specified by the application and not by this standard. This standard specifies the syntax, which addresses structure and properties of the telegram.

7.3 Structure of a telegram length of more than 7 B

A telegram with more than 7 B length has a field LENGTH larger than 6 B. It has a different structure and is able to transfer more information. It includes a data integrity checksum, and it can be repeated. Its structure is shown in

Figure 5.

LENGTH: This is the first field of the telegram and specifies the number of bytes of the telegram that follows this field. Its length is 1 B.

HDR: This field, the header, with a length 1 B, specifies (see Table 6)

• • the type of telegram,
• • if the field Extended Telegram Type (ETELTYP) is present,
• • if the field Extension Header (EXHDR) is present,
• • the length in bytes of the field source identity (ORIGID), and
• • if the field Destination Identity (DESTID) is present as well as its length in bytes.

EXHDR: This field, the Extension Header, of a length 1 B, specifies (see Table 7)

• • if the telegram is the original telegram,
• • if the telegram is a repeated telegram and then which order of repetition it is (maximum 15), and
• • if the telegram contains the field Additional Data (ADDATA) and then its length in bytes.

ETELTYP: This field, the extended telegram type, of a length 1 B, specifies additional types of telegram not included among those found in HDR (see Table 6).

ORIGID: This field specifies the identity of the source of the telegram. The length of this field is specified in the field HDR.

DESTID: This field specifies the identity of the device for which this telegram is intended. Its presence and length is specified in the field HDR (see Table 6).

DATA_DL: This field contains the payload of the data link layer. The length of this field has to be deduced from the value specified in the field LENGTH and presence and lengths of all the other fields in the telegram.

ADDATA: This field contains additional data, which can be used for testing and installation purposes. Its presence and length in bytes are specified in the field EXHDR (see Table 7).

HASH: This field, of length 1 B, contains the integrity check value. The algorithm is specified in 7.4.

ETELTYP specifies the telegram types 22 to 277. The semantics of a telegram type are specified by the application and not by this standard. This standard specifies the syntax, which addresses structure and properties of the telegram.

7.4 Data integrity

Data integrity is only provided for telegrams containing the field HASH, i.e. telegrams longer than 7 B. In order to check that one of these longer telegrams has arrived intact, a hash of the telegram is calculated by the transmitting device, i.e. a transmitter or a repeater, before transmission and attached to the telegram (field HASH). The attached hash value is not protected and thus only serves to detect transmission failures and not protection against malicious intent. The verification is done by the device receiving the telegram, i.e. a receiver or a repeater. The algorithm supported is an 8-bit long Cyclic Redundancy Check (CRC) algorithm. All receivers and repeaters are required to support this hash function.

If the verification of the intactness of the received telegram fails, the telegram is ignored.

The algorithm starts with the first byte after the field LENGTH of the telegram and calculates the remainder of the division (modulo 2) by the generator polynomial x⁸ + x² + x + 1 of the product x⁸ multiplied by the first byte of the telegram.

The result of this calculation is XORed with the next byte in the telegram and again the remainder of the division is calculated as above.

This procedure is repeated until the last byte preceding the field HASH of the telegram is reached. The remainder of the final division is used as hash value and is for a receiving device checked with the value in the field HASH and for a sending device inserted in the field HASH.

Annex A provides an example of an efficient C code implementation of this hash function algorithm.

8 Layer 3 – Network layer

8.1 Overview

The data unit in the network layer is also in the form of telegrams. The network layer is responsible for the timing when to transmit them. This access to media is described in 8.2. The network layer also handles the repeaters. Repeaters are inserted in an FMWSP protocol system when a direct transmission between a transmitter and its destination device cannot be made with sufficient quality. Some repeater requirements are described in 8.3 below.

8.2 Media access

8.2.1 General

The FMWSP is designed for networks operating with low duty cycles. It is assumed that each transmitter’s duty cycle is below 1 %. In this scenario collisions become very unlikely. The following two subclauses describe the possible ways of accessing the network.

8.2.2 Listen before talk

Listen-before-talk (LBT) is a technique used in wireless communications whereby a wireless transmitter or repeater first senses its wireless environment before starting a transmission. The aim is to avoid collisions with other senders. It is an optional feature of the transmitting device.

Prior to transmitting a telegram, the transmitting device checks whether there is an ongoing transmission. If this is the case, the transmission is suspended for a certain time. The process is described in the application specification for each application for which the FMWSP is used.

It is recommended to implement and use LBT before each telegram transmission, but it is not required. Some transmitting devices cannot support this feature such as some energy harvesting devices.

8.2.3 Random access

Random access is a process that allows a transmitter to access the network at any time it needs to transmit a telegram.

This method can be used if the transmitter is unable to detect if a transmission is currently going on. This happens if the transmitter has no receiver or if the energy to power the receiver is not available.

8.3 Repeater

Repeaters are necessary when the distance between sender and receiver is too large to establish an adequate wireless connection. The function of the repeater is to receive the telegram from the sender or another repeater and, if the value of the field LENGTH is larger than 6 and the first four bits of the EXHDR field of the telegram are different from ‘1111’, to send it again, so that the intended receiver of the message can get it, either directly or via another repeater. Each telegram is repeated only once even if it has received a telegram, the original or repeated, more than once.

It shall be possible to set a repeater so that it can have a lower value than 15 as its maximum repetition number. Before a repeater transmits a telegram it shall check the value of the repetition number of the incoming telegram. If it is larger or equal to the maximum value set for this repeater, the telegram is ignored. Otherwise, the telegram is repeated after incrementing the value of the repetition number in the first four bits of the EXHDR field. The value in the field ORIGID is not changed. It is noted that since the repeater changes the repetition number in the telegram it needs to calculate a new hash value in the data link layer (see 7.4).

In order to limit the amount of repeated telegrams in an environment, it is recommended that the number of repeaters be limited and also that the maximum telegram repetition number be limited for each repeater. The number of repeaters should be chosen as small as possible but in such a way that they fully support the environment of the system.

Bibliography