Two-way (true full-duplex) wireless

Abstract

Current wireless systems are one-way (similar to walkie-talkies), meaning that disjoint time or frequency segments are used to transmit and to receive. Realization of two-way wireless has challenged the research community for many years. This article1 establishes the theory and presents practical realization of two-way (true full-duplex) wireless. In contrast to the widely accepted beliefs, it is shown that two-way wireless is not only feasible, but is fairly simple, with virtually no degradation in signal-to-noise-ratio2. The innovation is in the antenna design and multiple levels for cancelling self-interference. Methods are developed to support Multiple-Input Multiple-Output (MIMO) two-way transmission, and asynchronous two-way links (useful in networking applications). The developed hardware uses off-the-shelf components, antennas have a simple structure, are omnidirectional (can be directional, if needed), do not suffer from bandwidth limitations, have a small size/spacing, and the increase in overall complexity is minimal. It is shown that two-way wireless can do more than doubling the rate. In particular: 1) Facilitates wireless networking. In particular, the ability to handle asynchronous users enables superimposing a half-duplex, low bit rate, low power, easy to detect network for control signaling superimposed (physical overlay, rather than logical) on top of the network of primary full-duplex data links. The superimposed links are separated from the primary full-duplex data links in the code domain, and use time multiplexing plus Carrier Sense Multiple Access (CSMA) among themselves. However, the conventional problems of CSMA are avoided as control links operate in parallel with primary full-duplex data links. The physical layer of control links is designed such that full-duplex data links can detect and cancel the interference caused by the superimposed control links. 2) Enhances security through desirable jamming. 3) Provides the ground to realize unconditional security (beyond computational or information theoretical security), using a simple method introduced in this article. 4) Facilitates multi-node distributed & collaborative signaling, including realization of Network Information Theoretic setups, and cognitive wireless. 5) Exploiting feedback, it improves point-to-point throughput, and enables ultra low power transmission. 6) Doubles the point-to-point throughput.