On the Degrees of Freedom of the Large-Scale Interfering Two-Way Relay Network

Abstract

Achievable degrees-of-freedom (DoF) of the large-scale interfering two-way relay network is investigated. The network consists of K pairs of communication nodes (CNs) and N relay nodes (RNs). It is assumed that K ≪ N and each pair of CNs communicates with each other through one of the N relay nodes without a direct link between them. Interference among RNs is also considered. Assuming local channel state information (CSI) at each RN, a distributed and opportunistic RN selection technique is proposed for the following three promising relaying protocols: amplifyforward, decode-forward, and compute-forward. As a main result, the asymptotically achievable DoF is characterized as N increases for the three relaying protocols. In particular, a sufficient condition on N required to achieve the certain DoF of the network is analyzed. Through extensive simulations, it is shown that the proposed RN selection techniques outperform conventional schemes in terms of achievable rate even in practical communication scenarios. Note that the proposed technique operates with a distributed manner and requires only local CSI, leading to easy implementation for practical wireless systems. Index TermsDegrees-of-freedom (DoF), interfering two-way relay channel, two-way K × N × K channel, local channel state information, relay selection. On the other hand, there have been few schemes that consider a general interfering TWR network which consists of K pairs of CNs and N RNs, also known as K × N × K interfering TWR networks. In [1], Rankov and Wittneben showed that the amplify-and-forward (AF) relaying protocol with interference-neutralizing beamforming can achieve the optimal 1 DoF of the half-duplex K × N × K interfering TWR network if N ≥ K(K − 1) + 1 for a given K. However, the scheme in [1] requires global CSI at all nodes and full collaboration amongst all RNs. The authors of [8], [9] considered the achievable degrees-of-freedom of K × K × K interfering OWR networks, where the number of CNs and RNs are the same. In particular, the interference neutralization technique of [1] was combined with the interference alignment technique to achieve the optimal DoF of the 2×2×2 interfering OWR network [8] . However, the scheme in [8] cannot be applied to the general K × N × K interfering TWR network with arbitrary numbers of K and N. In addition, the scheme in [8] works only with global CSI assumption at each node.The internet-of-things (IoT) concept has recently received much attection from wireless researchers, where an extremely large number of devices are expected to exist. In addition, the fifth generation (5G) cellular network is expected to support more than 10,000 devices, each of which can communicate directly with others or operate as a relay [10]. Among many devices, a small number of devices may transmit at a time due to sparse traffic pattern in the IoT scenario. Several studies have defined and studied the (N, K)-user interference channel (N ≫ K), in which K user pairs are selected to communicate at a time [11], [12].In...

Maximising the degrees of freedom of the physical‐layer secured relay networks with artificial jamming

“…Inspired by a recent paradigm shift in wireless communications focusing on the limiting performance, instead of maximising the secrecy rate directly, we propose to derive the maximum DoF of the secrecy capacity and attain the closed‐form solution that can achieve the full DoF [22]. The DoF‐optimal solution is asymptotically capacity optimal in high SNR regimes and has been widely considered in the literature [10, 22, 23] as it typically works very well in moderate SNR regions. More specifically, we first derive the DoF of the secrecy capacity that dominates the exact secrecy capacity in the high SNR regime, where the result is new to our knowledge.…”