LAN over power line

Introduction

Nowadays, practically every home and small office local area network use the WiFi as an access technology. Sometimes, also the classical Ethernet cables are used, but their application is uncomfortable and messy. Also, it is very hard to connect devices placed in different rooms or on different floors using the Ethernet cable. In case of large multi floor houses, it is not possible to provide good WiFi reception in all places. The idea of LAN over power-line solutions is to use the electrical wiring instead of the Ethernet cables.

The PowerLine Communication systems are not something new. In 1922, the high-tension lines was used for telemetry data transmission. The first consumer product was available around 1940 and the PowerLine Communication idea was applied in baby alarms. However, the first local area network applications could be possible thanks to HomePlug standard, which was released in June 2001.

HomePlug 1.0 and HomePlug AV standards

All currently available LAN over power line solutions use the IEEE 1901 standard family, i.e. the HomePlug. These standard are developed and promoted by HomePlug Powerline Alliance organisation, which wants to provide easy in use and fast PowerLine Communication system for home users. The first standard, which was released in June 2001, is called HomePlug 1.0 and offers up to 14 Mbps physical speed rate. It was very slow, so the improved version (Home Plug 1.0 Turbo) with 85 Mbps PHY-rate was introduced later.

However, this was still too slow in order to provide audio and video services from the electrical outlet. Therefore, the HomePlug AV (AV stands for Audio and Video) was specified and introduced in August 2005. The throughput increased significantly from 85 Mbps to 200 Mbps. However, it is only the physical layer data rate. The achievable maximum speed for user data is between 22 Mbps and 55 Mbps. Some of commercial available devices which are compatible with HomePlug AV standard use the wider bandwidth and offer up to 500 Mbps PHY-rate. In this case, the maximum achievable user data transmission throughput varies from 80 Mbps to 250 Mbps.

HomePlug AV2 standard

The latest standard is called HomePlug AV2 and it was introduced in January 2012. The HomePlug Powerline Alliance has introduced:

· additional bandwidth 30 – 86 MHz (the HomePlug AV 200 Mbps device uses only 1.8 – 28 MHz frequencies),

· more efficient coding and modulation scheme (4096 QAM 8/9),

· MIMO with beamforming (all 3 electrical wires are used for data transmission).

The HomePlug AV2 standard introduces more efficient packet data transmission protocol, therefore it offers 20% higher throughput than the previous version of the standard. The first HomePlug AV2 compatible devices, which were available on the market, did not support MIMO transmission and they were offering up to 600 Mbps PHY-rate.

The MIMO mode uses all three electrical wires, i.e. the power, the neutral and the ground and it doubles the speed. Therefore, if you want to take an advantage of HomePlug AV2 1200 Mbps solution, you have to have the proper electrical installation. Currently, the maximum achievable user data throughput is about 390 Mbps.

Maximum throughput differences

Of course, not only Power Line Communication adapters are connected to the home electrical installation. Unfortunately, all electrical devices (TVs, fridges, washing machines, computers etc.) generate the noise which has an impact on the data transmission speed. For an example, also an energy saving lamp generates a lot of noise while it is turning on. Therefore, a lot of manufactures use a noise reduction filter which can improve the performance.

WiFi extension

HomePlug powerline networking technology is the perfect solution for people who have issue with WiFi network coverage in their homes. This problem may be solved in two ways. The first solution is the application of HomePlug adapter with integrated WiFi access point. So, you can install it in the dead spot and connect the second classical (i.e. without WiFi) powerline communication adapter near to the WiFi router.

The second usage scenario is very interesting. In most cases, there is no possibility to install the WiFi router in convenient place. Generally, the WiFi router will provide the best performance if it is installed in the centre of the house. Therefore, if the ISP (Internet Service Provider) uses the Ethernet technology then it is possible to extend the ISP cable using two HomePlug adapters. The first device is connected to ISP network and the second device is connected to the WAN port of WiFi router.

Security

Security aspect is very important in the LAN over power line solutions. Generally, everyone who has access to the outlet can connect to the network. This is very important problem in offices and multifamily houses. Sometimes also the electrical installation may not to have an isolation between flats. Therefore, HomePlug AV standard uses 128 bit AES encryption technique. It is possible to pair the powerline communication adapters using the security button or setting the password.

The connection is encrypted only between powerline communication devices and all adapters used in the same network have to be paired or configured with the same password. The connection between the HomePlug adapter and the computer (or other Ethernet device) is not encrypted.