Physical layer network coding (PNC) is a relatively new technique that can perform network coding at the physical layer to boost the capacity of wireless ad hoc networks. By viewing overlapping data transmissions as their linear combinations, PNC can potentially achieve large improvement in physical-layer throughput over traditional transmissions and digital network coding at the higher layers. While existing research on PNC usually focuses on simple network topologies (e.g, the two-way relay channel), it appears natural and promising to further explore the opportunities of applying PNC in a large, general, multi-hop wireless network. This thesis covers two endeavours along this direction.
Firstly, we show how PNC can be combined with signal alignment (SA), another technique inspired from interference alignment (IA), for application in MIMO wireless networks. PNC coupled with SA (PNC-SA) has the potential of fully exploiting the precoding space at the senders, and can better utilize the spatial diversity of a MIMO network for higher transmission rates, outperforming existing techniques including MIMO or PNC alone, interference alignment (IA), and interference alignment and cancelation (IAC). We study the optimal precoding and power allocation problem of PNC-SA, for SNR maximization at the receiver. The mapping from SNR to BER is then analyzed, revealing that the throughput gain of PNC-SA does not come with a sacrifice in BER. Furthermore, the maximum throughput for the general N-user M-antenna uplink system is presented. We also demonstrate general applications of PNC-SA beyond a multi-user wireless uplink, and show via network level simulations that it can substantially increase the throughput of unicast and multicast sessions, by opening previously unexplored so- lution spaces in multi-hop MIMO routing.
Secondly, we focus on routing algorithm design in NanoNets, which are networks of nanomachines at extremely small dimensions, on the order of nanometers or micrometers.
Based on the salient features of a NanoNet, including low node cost and very low available power, we propose a new routing paradigm for unicast and multicast data transmission in NanoNets. Our design, termed Buddy Routing (BR), is enabled by PNC, and argues for pair-to-pair data forwarding in place of traditional point-to-point data forwarding. Through both analysis and simulations, we compare BR with point-to-point routing, in terms of raw throughput, error rate, energy efficiency, and protocol overhead, and show the advantages of BR in NanoNets.