Protocol coding for reliable wireless bits under jamming: Concept and experimental validation

Practical digital communication systems are designed to operate well in typical conditions, where the bit/packet error rates are below a certain level. In packet-based systems, if Bob has a data to send to Alice then Bob first transmits a preamble/packet header followed by data. A necessary condition to receive the data correctly is to receive the packet header and therefore headers use a more robust encoding. Under typical conditions, the probability of error for the packet header is close to 0. However, when the received signal at Alice is very weak or she experiences excessive interference, the error rate for the data part of the packets goes to 1, while the error rate for the header part increases significantly. This causes the wireless connection to break and produces a rate waterfall effect in digital systems: either the wireless data rate is above a minimal rate R, or it is equal to 0. In other words, practical digital systems do not degrade the data rate gracefully towards 0 as the transmission conditions worsen. We have recently introduced the concept protocol coding to refer to strategies for sending information by using the degrees of freedom available when one needs to decide the actions taken by a particular communication protocol. Under typical operating conditions, protocol coding delivers relatively low data rate, but the transmitted bits are very reliable. In this paper we show that by applying protocol coding, the rate waterfall effect can be avoided in practically any wireless digital communication system. An example application of such a concept is the case in which a short critical message needs to be delivered to a severely interfered receiver. We describe an experimental setup which proves the viability of this concept in a WiFi system exposed to a commercial jammer of the ISM band.