## 2 PLC Technologies
### Prime  
PRIME is a second-generation NBPLC technology that was initially developed by the PRIME Alliance [37], led by DSO and chipset manufacturers such as Iberdrola, Gas Natural Fenosa, Texas Instruments or ADD (now Microchip), and later standardized by ITU-T [38]. The standard specifies the two lowest layers of the protocol stack, namely: the PHY (physical) and the DLL (Data Link Layer). The DLL comprises in turn the MAC (Medium Access Control) and the Convergence Layer, which deals with multiplexing upper layer protocols, as well as with flow control and ARQ (Automatic Repeat reQuest) mechanisms. At the PHY layer, PRIME can operate at the CENELEC-A band (notably, between 41 and 89 kHz) or at the FCC/ARIB band (reaching up to 500 kHz) using OFDM (Orthogonal Frequency Division \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Technology** & **Promoter** & **Standard** & **Band** & **Modulation** & \
\begin{tabular}{c} **PHY Max Data** \\ **Rate (kbps)** \\ \end{tabular} &
\begin{tabular}{c} **Main** \\ **Deploments [50]** \\ \end{tabular} \\ \hline
**OSGP** & Echelon & IEC & CENELCA & \
\begin{tabular}{c} \\ 14908.1 \\ \end{tabular} & Single carrier & 3.6 &
\begin{tabular}{c} Nordic countries \\ and Russia \\ \end{tabular} \\ \hline
**CX1** & Siemens & \
\begin{tabular}{c} \\ 50590 \\ \end{tabular} & CENELCA &
\begin{tabular}{c} Multicarrier \\ (AMC-SS) \\ \end{tabular} & 64 & Austria \\ \hline
**Meters \& More** & ENEL &
\begin{tabular}{c} \\ 50568-4 \\ \end{tabular} & CENELCA & Single carrier & 9.6 & Italy, Spain \\ \hline
**G3-PLC** & G3 Alliance (EDF) & ITU-T & CENELCA & Multicarrier & 34 & France \\ \hline
**PRIME** & \
\begin{tabular}{c} PRIME Alliance \\ (Iberdrola, Gas \\ Natural Fenosa) \\ \end{tabular} & ITU-T & CENELCA & Multicarrier &
\begin{tabular}{c} \\ (OFDM) \\ \end{tabular} & 128.6 (v1.3.6) & Spain, UK \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of Narrowband PLC (NBPLC) technologies. Multiplexing). The carriers may use different modulation schemes allowing for maximum PHY data rates of up to 130 kbps, in the CENELEC-A band (version 1.3.6), and up to 1 Mbps, in the FCC/ARIB band (version 1.4). However, currently all PRIME deployed networks are compliant with version 1.3.6 (which is the version considered in this paper) and use DBPSK (Differential Binary Phase Shift Keying) with FEC (Forward Error Correction) ON, which is the most robust modulation scheme, allowing maximum PHY data rates of 24.1 kbps [38]. In DBPSK, the first carrier of the OFDM symbol carries a value that is well-known by transmitter and receiver and the information is encoded in the phase shift with respect to that value. Therefore, this modulation scheme avoids using an equalizer at the expense of slightly worsening the effective data rate and the BER (Bit Error Rate) vs. SNR (Signal-to-Noise Ratio) curve. At MAC layer, two kinds of nodes are defined: Base Node and Service Node. The Base Node (the so-called concentrator in AMI terminology) coordinates the PRIME network, only a single Base Node per network being allowed. The Service Nodes are the smart meters in AMI terminology. However, they may play just the role of Terminal or they can be promoted to Switches. Switches are communications repeaters whose main goal is to increase signal range in the cable via relaying, thus mitigating the effects of attenuation and noise. Figure 2 illustrates the different states and transitions of a Service Node together with the tree-wise logical topology of a PRIME network. Media access control in PRIME includes a SCP (Shared Contention Period) and a CFP (Contention Free Period). Their main difference is that in the former all the service nodes can content for the channel at the same time using CSMA-CA (Carrier Sense Multiple Access with Collision Avoidance); whereas the latter guarantees a time slot for service nodes and the base node to use the channel.