On the Synchronization of Physical-Layer Network Coding

Abstract

When data are transmitted in a wireless network, they reach the target receiver as well as other receivers in the neighborhood. Rather than a blessing, this attribute is treated as an interference-inducing nuisance in most wireless networks today (e.g., IEEE 802.11). Physical-layer network coding (PNC), however, has been proposed to take advantage of this attribute. Unlike "conventional" network coding which performs coding arithmetic on digital bit streams after they are decoded, PNC makes use of the additive nature of simultaneously arriving electromagnetic (EM) waves and applies the network coding arithmetic at the physical layer. As a result, the destructive effect of interference is eliminated and the capacity of networks is boosted significantly. A key requirement of PNC is synchronization among nodes, which has not been addressed previously. This is the focus of this paper. Specifically, we investigate the impact of imperfect synchronization (i.e., finite synchronization errors) on PNC. We show that with BPSK modulation, PNC still yields significantly higher capacity than straightforward network coding when there are synchronization errors. And interestingly, this remains to be so even in the extreme case where synchronization is not performed at all.

Compute-and-forward for two-way relay

“…In the simulation, 2 Z lattice code of 2 points per-dimension is employed in the two source nodes, which is equivalent to 4-QAM constellation. At the relay node, lattice decoding is used to decode the integer linear combination of the codewords sent from the two users.…”

“…The principle of network coding is that intermediate nodes forward functions of received packets rather than individual packets to increase the throughput. In 2006, three research groups [2]- [4] independently proposed the idea of PNC for wireless network. It is shown that, with a relay decoding and forwarding the modulo-two sum (XOR) of the transmitted packets, the throughput of a two-way relay channel can be significantly improved.…”

Collision Codes: Decoding Superimposed BPSK Modulated Wireless Transmissions

“…Using a suitable mapping scheme, they show that for certain modulation schemes, there exists a mapping scheme such that the relationship between the two transmitted binary bits and the decoded binary bit follows the XOR principle. We here revisit the PNC operation [1] and its mapping scheme to achieve the XOR principle. Consider two senders, N 1 and N 3 , and a common receiver N 2 .…”

“…For BPSK, we have a j = 2s j − 1 [1]. At N 2 , a scheme (see Table I) that maps a strong energy signal to binary 0 (i.e.…”

Analog Network Coding for chain topology in non-mutual transmission

“…Nevertheless, the amount of improvement is different due to applying different NC schemes, which encourages researchers to work on this field. In this regard, Physical-layer Network Coding (PNC or PLNC) [19] and Analog Network Coding (ANC) [20] were devised to attain more capacity by exploiting simultaneous transmission.…”