# State of the Art and Trends Review of _Smart Metering_ in Electricity Grids
## 3 Smart Metering Technologies
In addition, cellular technology has experienced a rapid growth, resulting in better bit rates and more potential applications. However, individual connections are still expensive. Several U.S. carriers such as T-Mobile and Verizon have adopted _4G Long Term Evolution_ (_LTE_) since the cost of upgrading the existing _3G_ network is lower [11]. Despite the fact that most European countries use wired alternatives, cellular networks, especially _GPRS_, can also be found in some deployments [29]. _GPRS_ is an open standard technology and an effective and reliable technology. Several trials performed in Cork (Ireland) with _SM_s using _GPRS_ reported a good performance of this technology (success rate of 97.89% for first-time reads) and easy deployment [30]. However, the data rate is moderate. Other wireless technologies such as _ZigBee_, _6 LoWPAN_, and _Bluetooth_ are based on _IEEE 802.15_ standard [31]. These technologies are characterized by low bit rates, low power consumption, and low cost. _ZigBee_ is a widely-known technology and the most used in domestic networks so far. It is considered a good option for _Smart Metering_ and energy management due to its simplicity, mobility, robustness, low bandwidth requirements, and low cost of deployment [32]. However, the limited size of the devices that implement _ZigBee_ restrict the battery life, the internal memory, and the processing capabilities. On the other hand, _6 LoWPAN_ uses the _Internet Protocol_ (_IP_) over _WPAN_ (_IPv6 over Low Power Wireless Personal Area Networks_). Since it is based on the same features as _ZigBee_, they compete with each other in the same market. The main advantage of _6 LoWPAN_ is that it identifies every node by means of an _IP_ address, which allows ubiquity, versatility, and resilience [33]. As an example, [PERSON] _et al._ present in [34] both a _ZigBee_-based and a _6 LoWPAN_-based _SM_ network architecture. Finally, _Bluetooth_ is a low-power and short-range option, mostly used in local applications. It allows both point-to-point and point-to-multi-point configurations. Despite being less used, _Bluetooth_ technology can be a possible option for communication of control signals and transmitting energy consumption data. [PERSON] _et al._ proposed in [35] a _Bluetooth_ based energy meter that can collect and transmit the energy consumption data wirelessly to a central base station. However, this provides a lower degree of security in comparison with other technologies [36]. Another family of standards is _IEEE 802.11_ (see Table 3) or _Wireless Neighborhood Access Network_ (_WNAN_), also known as _wireless Ethernet_[37]. They are technologies with a high degree of reliability and availability (although lower than wired options). However, the electromagnetic interferences affect their data rate and the radiofrequency that they emit may influence surrounding devices. Finally, _Worldwide inter-operability for Microwave Access_, _WiMAX_, comes from _IEEE 802.16_ standard for _Wireless Metropolitan Area Networks_ (_WMAN_) and is a complementary technology to _IEEE 802.11_ standard. _WiMAX_ is able to supply to thousands of end-users at larger distances and with better _QoS_ systems [36]. Some U.S. companies are proposing _WiMAX_ for _SG_ solutions and _WiMAX_ has also been used as a backhaul in a wide Smart Metering deployment in Australia [38]. However, it is still an expensive technology. Among the existing wired technologies for _Smart Metering_ systems, _Power Line Communication_ (_PLC_) is one of the most widespread technologies and the most used in Europe and China [39]. A great advantage of _PLC_ is that the communication channel is part of the electricity grid, and therefore it is already deployed. Additionally, transmitter devices do not depend on batteries since they use the power supply directly [40].