Unlike twisted-pair (used in DSL) or shielded coaxial cable, power lines have no inherent noise cancellation mechanism. In order to cope up with noisy environment of power lines, OFDM along with a number of channel interference noise ratio based modulations such as QAM, BPSK and QPSK may be a solution. OFDM is very robust against frequency selectivity but any time-varying characteristic of the channel limits system performance. Time variations deteriorate the orthogonality of the sub-carriers, resulting in inter-carrier interference. To eliminate inter-carrier interference, a guard time is inserted with a length longer than the duration of the impulse response of the channel. The insertion of guard time has the penalty of a loss in the signal-to-noise ratio that further increases the bandwidth requirement.
Bandwidth issues. Each distribution transformer feeds power to 10 to 50 houses/offices. Since bandwidth to the transformer is limited and the same power line is shared by all these houses, there is scarcity of bandwidth available to each customer. Moreover, BPL is a contention-based system (CSMA/CA), which again imposes additional challenges. Similar to DSL, speeds (bit-rates) of BPL systems available to customers are also dependent on the distance between the supplying substation and the customer’s home.
Security issues. BPL signal propagates in a LAN-like manner, which makes detection and interception of neighbouring transmissions simple. So in order to prevent interception of legitimate customers’ data by unauthorised intruders, strong authorisation, authentication and data encryption algorithms such as DES and AES should be used.
BPL in a nutshell
BPL technology is a union of two applications in a single system, holding great promise as a ubiquitous broadband solution that would offer a viable alternative to cable, digital subscriber line, fibre and wireless broadband solutions. Additionally, it offers the ability to employ intelligent power line networks that make use of supervisory control and data acquisition devices. As standardisation, interference mitigation and improvement in technology are on their way, the future of BPL looks very bright.
The author is a junior telecom officer at Bharat Sanchar Nigam Limited, currently working in Ludhiana, Punjab. He holds Ph.D in electronics engineering from Indian Institute of Technology, BHU, Varanasi, and has authored and co-authored several research papers in peer-reviewed national/international journals including IEEE and conference proceedings. His current research interests include wired and wireless technologies for high-speed Internet access; use of renewable energy sources; and analysis, design and simulation of high-power high-frequency microwave devices and systems for communication purposes