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International audience; We consider a communication system in which two sources communicate with a destination with the help of a common relay. We assume that the relay operates in half-duplex mode; and concentrate on the symmetric-rate case. We study and analyse the performance of a simple strategy in which the relay simply amplifies its output and retransmits it. However, unlike standard amplify-and-forward, the destination recovers the sent messages by computing and inverting two appropriate linear combinations of the sources' messages, obtained using what it gets from the sources and the relay. We discuss the design criteria and establish the sum-rate allowed by this strategy. Also, we consider, and solve, the problem of maximizing the sum-rate by properly optimizing the power values and the integer-valued coefficients of the recovered linear combinations. It should be emphasized that although the coding strategy described in this paper performs only as good as standard amplify-and-forward, it has the advantage of utilizing simpler linear codes; and, so, is more relevant in practical collaborative systems.

We consider a two-user state-dependent multiaccess channel in which the states of the channel are known non-causally to one of the encoders and only strictly causally to the other encoder. Both encoders transmit a common message and, in addition, the encoder that knows the states non-causally transmits an individual message. We find explicit characterizations of the capacity region of this communication model in both discrete memoryless (DM) and memoryless Gaussian cases. In particular the capacity region analysis demonstrates the utility of the knowledge of the states only strictly causally at the encoder that sends only the common message in general. More specifically, in the DM setting we show that such a knowledge is beneficial and increases the capacity region in general. In the Gaussian setting, we show that such a knowledge does not help, and the capacity is same as if the states were completely unknown at the encoder that sends only the common message. The analysis also reveals optimal ways of exploiting the knowledge of the state only strictly causally at the encoder that sends only the common message when such a knowledge is beneficial. The encoders collaborate to convey to the decoder a lossy version of the state, in addition to transmitting the information messages through a generalized Gel'fand-Pinsker binning. Particularly important in this problem are the questions of 1) optimal ways of performing the state compression and 2) whether or not the compression indices should be decoded uniquely. We show that both compression \`a-la noisy network coding, i.e., with no binning and non-unique decoding, and compression using Wyner-Ziv binning with backward decoding and non-unique or unique decoding are optimal., Comment: Submitted to the IEEE Transactions on Information Theory, 38 pages, 2 figures

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We consider a three-terminal state-dependent relay channel with the channel state noncausally available at only the relay. Such a model may be useful for designing cooperative wireless networks with some terminals equipped with cognition capabilities, i.e., the relay in our setup. In the discrete memoryless (DM) case, we establish lower and upper bounds on channel capacity. The lower bound is obtained by a coding scheme at the relay that uses a combination of codeword splitting, Gel'fand-Pinsker binning, and decode-and-forward relaying. The upper bound improves upon that obtained by assuming that the channel state is available at the source, the relay, and the destination. For the Gaussian case, we also derive lower and upper bounds on the capacity. The lower bound is obtained by a coding scheme at the relay that uses a combination of codeword splitting, generalized dirty paper coding, and decode-and-forward relaying; the upper bound is also better than that obtained by assuming that the channel state is available at the source, the relay, and the destination. In the case of degraded Gaussian channels, the lower bound meets with the upper bound for some special cases, and, so, the capacity is obtained for these cases. Furthermore, in the Gaussian case, we also extend the results to the case in which the relay operates in a half-duplex mode., Comment: 62 pages. To appear in IEEE Transactions on Information Theory

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Publication in the conference proceedings of EUSIPCO, Glasgow, Scotland, 2009

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International audience; Multiple user information embedding is concerned with embedding several messages into the same host signal. This paper presents several implementable ''Dirty Paper Coding'' (DPC) based schemes for multiple user information embedding, through emphasizing their tight relationship with conventional multiple user information theory. We first show that depending on the targeted application and on whether the different messages are asked to have different robustness and transparency requirements or not, multiple user information embedding parallels one of the well-known multi-user channels with state information available at the transmitter. The focus is on the Gaussian Broadcast Channel (BC) and the Gaussian Multiple Access Channel (MAC). For each of these channels, two practically feasible transmission schemes are compared. The first approach consists in a straightforward- rather intuitive- superimposition of Dirty Paper Coding schemes. The second consists in a joint design of these Dirty Paper Coding schemes. This joint approach heavily relies on a recent work by Kim {\it et al.} in which the authors extend the single-user Costa's DPC to the multiple user case. The results in this paper extend the practical implementations QIM, DC-QIM and SCS that have been originally conceived for one user to the multiple user case. After presenting the key features of the joint design within the context of structured scalar codebooks, we broaden our view to discuss the framework of more general lattice-based (vector) codebooks and show that the gap to full performance can be bridged up using finite dimensional lattice codebooks. Performance evaluations, including Bit Error Rates and achievable rate region curves are provided for both methods, illustrating the improvements brought by a joint design.

A detection system with a single sensor and $\mathsf{K}$ detectors is considered, where each of the terminals observes a memoryless source sequence and the sensor sends a common message to all the detectors. The communication of this message is assumed error-free but rate-limited. The joint probability mass function (pmf) of the source sequences observed at the terminals depends on an $\mathsf{M}$-ary hypothesis $(\mathsf{M} \geq \mathsf{K})$, and the goal of the communication is that each detector can guess the underlying hypothesis. Each detector $k$ aims to maximize the error exponent under hypothesis $k$, while ensuring a small probability of error under all other hypotheses. This paper presents an achievable exponents region for the case of positive communication rate, and characterizes the optimal exponents region for the case of zero communication rate. All results extend also to a composite hypothesis testing scenario., Comment: 5 pages, 2 figures, accepted for presentation at the 2018 IEEE International Symposium on Information Theory (ISIT 2018), Jun. 2018, Vail Colorado

International audience; We consider a two-user state-dependent multiaccess channel in which the states of the channel are known, causally or only strictly causally, at both encoders, but not at the decoder. Both encoders transmit a common message and, one of the encoders also transmits an individual message. We study the capacity region of this communication model for both causal and strictly causal settings. For the model with causal states, we find an explicit characterization of the capacity region in the discrete memoryless case. For the model with strictly causal states, we establish inner and outer bounds on the capacity region. The outer bound is non-trivial, has a relatively simple form and has the advantage of incorporating only one auxiliary random variable. In particular, it suggests that there is none, or at best only little, to gain from having the encoder that transmits both messages also sending an individual description of the state to the receiver, in addition to the compressed version that is sent cooperatively with the other encoder. The results shed more light on the utility of delayed channel state information for increasing the capacity region of multiaccess channels; and tie with some recent progress in this framework.

International audience; We consider a two-user state-dependent multiaccess channel in which the states of the channel are known only strictly causally at both encoders, but not at the decoder. Both encoders transmit a common message and, one of the encoders also transmits an individual message. We study the capacity region of this communication model. We establish inner and outer bounds on the capacity region. The outer bound is non-trivial, and has a relatively simple form. Furthermore, we show that the inner and outer bounds coincide in some special case; and, so, we characterize the capacity region fully in these cases. The results shed more light on the utility of delayed channel state information for increasing the capacity region of multiaccess channels; and tie with some recent progress in this framework.

International audience; We study a system in which two sources communicate with a destination with the help of a half-duplex relay. We consider a decoding strategy, based on the compute-and-forward strategy, in which the destination decodes two integer-valued linear combinations that relate the transmitted codewords. In this strategy, the relay compresses its observation using Wyner- Ziv compression and then forwards it to the destination. The destination appropriately combines what it gets from the direct transmission and the relay. Then, using this combination, it computes two integer-valued linear combinations. We discuss the encoding/decoding strategy, and evaluate the achievable sumrate. Next, we consider the problem of allocating the powers and selecting the integer-valued coefficients of the recovered linear combinations in order to maximize the sum-rate. For the model under consideration, the optimization problem is NP hard. We propose an iterative algorithm to solve this problem using coordinate descent method. The results are illustrated through some numerical examples.

International audience; We study a special case of Willems's two-user multi-access channel with partially cooperating encoders from a security perspective. This model differs from Willems's setup in the following aspects - only one encoder, Encoder 1, is allowed to conference, Encoder 2 does not transmit any message, and there is an additional passive eavesdropper from whom the communication should be kept secret. For the discrete memoryless (DM) case, we establish inner and outer bounds on the capacity-equivocation region. The inner bound is established by a careful combination of Willems's coding scheme, noise injection scheme and additional binning that provides randomization for security. For the memoryless Gaussian model, we establish lower and upper bounds on the secrecy capacity. We also studied some extreme cases of cooperation between the encoders and showed that, under certain conditions, these bounds coincide.

International audience; We consider a multiple access relay channel (MARC), in which a relay, based on the recently proposed compute-and-forward protocol, helps two transmitters to communicate with a common destination. The relay decodes a linear combination of the received symbols instead of the individual symbols then forwards the new symbol to the destination. The destination recovers two linear equations from the decoded signals. The two equations relate the transmitted symbols with integer coefficients at different computational rates. We propose an iterative algorithm to optimize the integer coefficients and the power allocation at the transmitters alternatively, so that the sum-rate is maximized. In each iteration, the integer coefficients are updated by solving a mixed-integer quadratic programming (MIQP) problem with quadratic constraints, while the power allocation is updated by solving a series of geometric programs using a successive convex approximation method. The simulation results show that the compute-and-forward strategy and the proposed optimization method can offer substantial gain over the standard amplify-and-forward and decode-and-forward protocols for this model.

International audience; Abstract--In this work1, we study a multiaccess relay channel (MARC). The system consists of two transmitters communicating with a destination with the help of a half-duplex relay. We extend and adapt the recently proposed lattice-based computeand- forward coding scheme to the model we study. This coding scheme can be seen as a form of some network-coding that is implemented at the relay through modulo-reduction. In this scheme, the destination decodes two linear equations with integer coefficients that relate the transmitted symbols at different computational rates. First, we discuss the design criteria, and derive the allowed computation rate. Then, we optimally allocate the different parameters by solving a series of geometric programs using successive convex approximation methods. The analysis shows that our coding scheme can offer substantial gain over the standard amplify-and-forward and decode-and-forward for this model. We illustrate our results through some numerical examples.

We study a four terminal parallel relay-eavesdropper channel which consists of multiple independent relay-eavesdropper channels as subchannels. For the discrete memoryless case, we establish inner and outer bounds on the rate-equivocation region. For each subchannel, secure transmission is obtained through one of the two coding schemes at the relay: decoding-and-forwarding the source message or confusing the eavesdropper through noise injection. The inner bound allows relay mode selection. For the Gaussian model we establish lower and upper bounds on the perfect secrecy rate. We show that the bounds meet in some special cases, including when the relay does not hear the source. We illustrate the analytical results through some numerical examples., 8 pages, Presented at the Forty-Eighth Annual Allerton Conference on Communication, Control, and Computing, September 29 - October 1, 2010, Monticello, IL, USA

We1 consider the problem of two transmitters would like to communicate with a destination with the help of a half-duplex relay. In this work, we are presenting the advantages of using nested lattices for the AWGN channels. The sources map their messages using lattice code and then broadcast them to the relay and the destination. The relay receives two independent symbols at the same channel. The relay either combines the two symbols using lattice modulo and then decode or decode the two symbols separately also using modulo lattice, then forwards the new symbol to the destination. The destination tries to recover the two messages using different decoding strategies. One of the strategies is to recover two linear equations in function of the two received symbols with integer coefficients then, solve these equations to recover the two messages. The integer coefficients need to be optimally selected to reduce the noise at the receivers. The other strategy is to use successive decoding at the relay and the destination. This strategy outperforms the first when two integer coefficients are zero. The strategies are discussed and compared with the traditional DF (Decode and Forward). The simulation results show the advantages of using lattice codes and the improvement in rates for certain regimes.

We consider the problem of transmission over a relay version of the carbon-copying onto dirty paper. In this setup, additive Gaussian outside interferences corrupt both transmissions to the relay and to the destination; and only the source knows the interferences (in a noncausal manner). We first focus on the case of one interference corrupting both links; and then we focus on the case of two independent interferences. For each of these two models, we establish a lower bound on the channel capacity. The coding schemes for the lower bounds use techniques of dirty paper coding or carbon copying onto dirty paper, interference reduction at the source and decodeand-forward relaying. The results reveal that, by opposition to carbon copying onto dirty paper and its root Costa's initial dirty paper coding (DPC), it may be beneficial in our setup that the informed source uses a part of its power to partially cancel the effect of the interference so that the uninformed relay benefits from this cancellation, and so the source benefits in turn. The established results may be of importance for the emerging field of cooperation in presence of some cognitive radios that might be aware of some of other users messages intended to a common receiver.

We consider a two-user state-dependent multiaccess channel in which only one of the encoders is informed, non-causally, of the channel states. Two independent messages are transmitted: a common message transmitted by both the informed and uninformed encoders, and an individual message transmitted by only the uninformed encoder. We derive inner and outer bounds on the capacity region of this model in the discrete memoryless case as well as the Gaussian case. Further, we show that the bounds for the Gaussian case are tight in some special cases., 5 pages, Proc. of IEEE International Symposium on Information theory, ISIT 2009, Seoul, Korea

We consider a three-terminal Gaussian relay channel corrupted by a Gaussian interference. We assume that the interference is non-causally known to only some, i.e, not to all, the terminals. We examine two different scenarios: 1) both the source and the relay, but not the destination, know the interference and collaborate to cancel out its effect and 2) only the source knows the interference. The first scenario exhibits some symmetry and we refer to it as “informed source and relay”. The second scenario exhibits some asymmetry and we refer to it as “informed source only”. For the Gaussian relay channel with informed source and relay, we derive a lower bound on channel capacity, based on the source and the relay both employing standard dirty paper coding (DPC) and the relay using the decode-and-forward scheme. We also show that this lower bound meets with the cut-set bound, and thus gives capacity, if the channel is degraded. For the Gaussian relay channel with informed source only, we derive a lower bound on channel capacity. This lower bound is based on a generalized DPC that consists in a combination of partial cancellation of the known interference and standard DPC. In the asymmetric scenario, the performance characterizations reveal that, by opposition to Costa's initial DPC, it may be beneficial that the informed source uses a part of its power to (partially) cancel the effect of this interference so that the uninformed relay benefits from this cancellation.

International audience; Cooperative information embedding deals with the problem of embedding unperceived information into some cover signal by different users or partners, cooperatively. It models applications in which embedded signals, or watermarks, transmitted over wireless networks need to be reinforced in order to withstand channel impairments. In cooperative information embedding, each of the embedders who can reinforce the embedded signal may or may not know the original cover signal. In this paper we concentrate on the two user case: an initial embedder and an assisting embedder or helper collaborate to embed some watermark into a given digital media content which is transmitted over a wireless network. One important application is that of infrastructure-aided information embedding, a case in which the network provider plays the role of a helper and contributes to securing the distribution of the media, not only by blocking unauthorized signals but also by reinforcing the watermarks in legitimate signals. We investigate the two scenarios in which the helper knows or not the cover signal. For each of these scenarios we derive lower and upper bounds on channel capacity. Furthermore, we also design implementable coding schemes and derive the embedding rates practically allowed by these schemes, for both scenarios. Among others, the performance characterization shows that, for cooperative information embedding to be effective, careful code design is required at both the initial embedder and the helper. The careful design concerns the joint conception of the embedded codes as well as the exploitation of the knowledge of the cover signal, if any.

In this work, we consider a partially cooperative relay broadcast channel (PC-RBC) controlled by random parameters. We provide rate regions for two different situations: 1) when side information (SI) S^n on the random parameters is non-causally known at both the source and the relay and, 2) when side information S^n is non-causally known at the source only. These achievable regions are derived for the general discrete memoryless case first and then extended to the case when the channel is degraded Gaussian and the SI is additive i.i.d. Gaussian. In this case, the source uses generalized dirty paper coding (GDPC), i.e., DPC combined with partial state cancellation, when only the source is informed, and DPC alone when both the source and the relay are informed. It appears that, even though it can not completely eliminate the effect of the SI (in contrast to the case of source and relay being informed), GDPC is particularly useful when only the source is informed., Comment: 7 pages, Proc. of IEEE International Symposium on Information theory, ISIT 2007, Nice, France