24,936 research outputs found
Asymptotic Analysis on Spatial Coupling Coding for Two-Way Relay Channels
Compute-and-forward relaying is effective to increase bandwidth efficiency of
wireless two-way relay channels. In a compute-and-forward scheme, a relay tries
to decode a linear combination composed of transmitted messages from other
terminals or relays. Design for error correcting codes and its decoding
algorithms suitable for compute-and-forward relaying schemes are still
important issue to be studied. In this paper, we will present an asymptotic
performance analysis on LDPC codes over two-way relay channels based on density
evolution (DE). Because of the asymmetric nature of the channel, we employ the
population dynamics DE combined with DE formulas for asymmetric channels to
obtain BP thresholds. In addition, we also evaluate the asymptotic performance
of spatially coupled LDPC codes for two-way relay channels. The results
indicate that the spatial coupling codes yield improvements in the BP threshold
compared with corresponding uncoupled codes for two-way relay channels.Comment: 5 page
Joint Compute and Forward for the Two Way Relay Channel with Spatially Coupled LDPC Codes
We consider the design and analysis of coding schemes for the binary input
two way relay channel with erasure noise. We are particularly interested in
reliable physical layer network coding in which the relay performs perfect
error correction prior to forwarding messages. The best known achievable rates
for this problem can be achieved through either decode and forward or compute
and forward relaying. We consider a decoding paradigm called joint compute and
forward which we numerically show can achieve the best of these rates with a
single encoder and decoder. This is accomplished by deriving the exact
performance of a message passing decoder based on joint compute and forward for
spatially coupled LDPC ensembles.Comment: This paper was submitted to IEEE Global Communications Conference
201
Weak Secrecy in the Multi-Way Untrusted Relay Channel with Compute-and-Forward
We investigate the problem of secure communications in a Gaussian multi-way
relay channel applying the compute-and-forward scheme using nested lattice
codes. All nodes employ half-duplex operation and can exchange confidential
messages only via an untrusted relay. The relay is assumed to be honest but
curious, i.e., an eavesdropper that conforms to the system rules and applies
the intended relaying scheme. We start with the general case of the
single-input multiple-output (SIMO) L-user multi-way relay channel and provide
an achievable secrecy rate region under a weak secrecy criterion. We show that
the securely achievable sum rate is equivalent to the difference between the
computation rate and the multiple access channel (MAC) capacity. Particularly,
we show that all nodes must encode their messages such that the common
computation rate tuple falls outside the MAC capacity region of the relay. We
provide results for the single-input single-output (SISO) and the
multiple-input single-input (MISO) L-user multi-way relay channel as well as
the two-way relay channel. We discuss these results and show the dependency
between channel realization and achievable secrecy rate. We further compare our
result to available results in the literature for different schemes and show
that the proposed scheme operates close to the compute-and-forward rate without
secrecy.Comment: submitted to JSAC Special Issue on Fundamental Approaches to Network
Coding in Wireless Communication System
Code Design for Multihop Wireless Relay Networks
We consider a wireless relay network, where a transmitter node communicates with a receiver node with the help of relay nodes. Most coding strategies considered so far assume that the relay nodes are used for one hop. We address the problem of code design when relay nodes may be used for more than one hop. We consider as a protocol a more elaborated version of amplify-and-forward, called distributed space-time coding, where the relay nodes multiply their received signal with a unitary matrix, in such a way that the receiver senses a space-time code. We first show that in this scenario, as expected, the so-called full-diversity condition holds, namely, the codebook of distributed space-time codewords has to be designed such that the difference of any two distinct codewords is full rank. We then compute the diversity of the channel, and show that it is given by the minimum number of relay nodes among the hops. We finally give a systematic way of building fully diverse codebooks and provide simulation results for their performance
Wireless network coding for multi-hop relay channels
Future wireless communication systems are required to meet growing demands for high spectral e�ciency, low energy consumption and high mobility. The advent of wireless network coding (WNC) has o�ered a new opportunity to improve network throughput and transmission reliability by exploiting interference in intermediate relays. Combined with network coding and self-information cancelation, WNC
for two-way relay channels (TWRCs) has come to the forefront. This dissertation focuses on exploiting WNC in multi-hop two-way relay channels (MH-TRCs). Particularly, a multi-hop wireless network coding (MH-WNC) scheme is designed for the generalized L-node K-message MH-TRC. Theoretical studies on the network throughput and performance bounds achieved by the MH-WNC scheme with di�erent relaying strategies (i.e., amplify-and-forward
(AF) and compute-and-forward (CPF)) are carried out. Furthermore, by introducing di�erent numbers of transmission time intervals into the MH-WNC, a
multiple-time-interval (Multi-TI) MH-WNC is proposed to determine an optimal MH-WNC which can achieve the best outage performance for all-scale MH-TRCs.
Finally, this study extends the research on WNC one step forward from two-user networks to multi-user networks. An extended CPF joint with a dominated solution for maximizing the overall computation rate is proposed for the multi-way
relay channel (mRC) in the last chapter. The contributions of this dissertation are multifold. First, the proposed MHWNC scheme with fixed two transmission time intervals can achieve a significantly improved network throughput compared to the non-network coding (Non-NC) scheme in the generalized L-node K-message MH-TRC. Theoretical results
are derived for both multi-hop analog network coding (MH-ANC) and multi-hop compute-and-forward (MH-CPF). Moreover, both theoretical and numerical results demonstrate that the two MH-WNC schemes can be applied to different scale MH-TRCs to achieve a better outage performance compared to the conventional Non-NC scheme (i.e., MH-ANC for the non-regenerative MH-TRC with a small number of nodes, and MH-CPF for the regenerative MH-TRC with a large number of nodes.). Furthermore, a Multi-TI MH-WNC scheme is generalized with a special binary-tree model and characteristic matrix. The determined optimal MH-WNC scheme is able to provide the best outage performance and
outperform the Non-NC scheme in all scale MH-TRCs. Last but not least, this dissertation provides a preliminary investigation of WNC in mRCs. The proposed dominated solution for maximizing the overall computation rate can ensure that all the nodes in the mRC successfully recover their required messages. Moreover, the extended CPF strategy is proven superior to Non-NC in the mRC with a
small number of users
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