Yeow-Khiang Chia

Mobile Data Offloading Through A Third-Party WiFi Access Point: An Operator's Perspective

WiFi offloading is regarded as one of the most promising techniques to deal with the explosive data increase in the existing cellular network due to its high data transmission rate, and low requirement on devices. In this paper, we investigate the mobile data offloading problem through a third-party WiFi access point (AP) for a cellular mobile system. From the cellular operators perspective, by assuming the data offloaded through the third-party WiFi AP is charged based on usage, we formulate mobile data offloading problem as a utility maximization problem, which is an integer programming problem. A centralized mobile data offloading scheme is then obtained by considering its relaxation problem. It is strictly proved that the proposed centralized data offloading scheme is near-optimal when the number of users is large. Then, to relieve the computing burden on the cellular base station, we propose a threshold-based distributed data offloading scheme. We show that the proposed distributed scheme performs very well once the threshold is properly chosen.

Wiretap Channel With Causal State Information

A lower bound on the secrecy capacity of the wiretap channel with state information available causally at both the encoder and the decoder is established. The lower bound is shown to be strictly larger than that for the noncausal case by Liu and Chen. Achievability is proved using block Markov coding, Shannon strategy, and key generation from common state information. The state sequence available at the end of each block is used to generate a key to enhance the transmission rate of the confidential message in the following block. An upper bound on the secrecy capacity when the state is available noncausally at the encoder and the decoder is established and is shown to coincide with the aforementioned lower bound for several classes of wiretap channels with state.

Three-Receiver Broadcast Channels With Common and Confidential Messages

This paper establishes inner bounds on the secrecy capacity regions for the general three-receiver broadcast channel with one common and one confidential message sets. We consider two setups. The first is when the confidential message is to be sent to two receivers and kept secret from the third receiver. Achievability is established using indirect decoding, Wyner wiretap channel coding, and the new idea of generating secrecy from a publicly available superposition codebook. The inner bound is shown to be tight for a class of reversely degraded broadcast channels and when both legitimate receivers are less noisy than the third receiver. The second setup investigated in this paper is when the confidential message is to be sent to one receiver and kept secret from the other two receivers. Achievability in this case follows from Wyner wiretap channel coding and indirect decoding. This inner bound is also shown to be tight for several special cases.

3-Receiver broadcast channels with common and confidential messages

Achievable secrecy rate regions for the general 3-receiver broadcast channel with one common and one confidential message sets are established. We consider two setups: (i) when the confidential message is to be sent to two of the receivers and the third receiver is an eavesdropper; and (ii) when the confidential message is to be sent to one of the receivers and the other two receivers are eavesdroppers. We show that our secrecy rate regions are optimum for some special cases.

Wiretap channel with causal state information

A lower bound on the secrecy capacity of the wiretap channel with state information available causally at both the encoder and the decoder is established. The lower bound is shown to be strictly larger than that for the noncausal case by Liu and Chen. Achievability is proved using block Markov coding, Shannon strategy, and key generation from common state information. The state sequence available at the end of each block is used to generate a key to enhance the transmission rate of the confidential message in the following block. An upper bound on the secrecy capacity when the state is available noncausally at the encoder and the decoder is established and is shown to coincide with the aforementioned lower bound for several classes of wiretap channels with state.

Cascade, Triangular, and Two-Way Source Coding With Degraded Side Information at the Second User

We consider the Cascade and Triangular ratedistortion problems where the same side information is available at the source node and User 1, and the side information available at User 2 is a degraded version of the side information at the source node and User 1. We characterize the rate-distortion region for these problems. For the Cascade setup, we showed that, at User 1, decoding and re-binning the codeword sent by the source node for User 2 is optimum. We then extend our results to the Two way Cascade and Triangular settings, where the source node is interested in lossy reconstruction of the side information at User 2 via a rate limited link from User 2 to the source node. We characterize the rate distortion regions for these settings. Next, we evaluate our regions in the Quadratic Gaussian Cascade and Triangular settings, and obtain characterizations of these settings in the form tractable low dimensional optimization problems.

Multi-terminal source coding with action dependent side information

We consider multi-terminal source coding with a single encoder and multiple decoders where either the encoder or the decoders can take actions which affect the quality or availability of the side information present at the decoders, subjected to an additional cost constraint on the actions taken. For the scenario where a joint action is taken at the decoders, we characterize the rate-cost trade-off region for lossless source coding, and give an achievability scheme for lossy source coding for two decoders which is optimum for several special cases. For the case where the encoder takes actions, we characterize the rate-cost trade-off for a class of lossless source coding scenarios with multiple decoders.

Estimation with a helper who knows the interference

We consider the problem of estimating a signal corrupted by independent interference with the assistance of a cost-constrained helper who knows the interference causally or noncausally. When the interference is known causally, we characterize the minimum distortion incurred in estimating the desired signal. In the noncausal case, we present a general achievable scheme for discrete memoryless systems and novel lower bounds on the distortion for the binary and Gaussian settings. Our Gaussian setting coincides with that of assisted interference suppression introduced by Grover and Sahai. Our lower bound for this setting is based on the relation recently established by Verdú between divergence and minimum mean squared error. We illustrate with a few examples that this lower bound can improve on those previously developed. Our bounds also allow us to characterize the optimal distortion in several interesting regimes. Moreover, we show that causal and noncausal estimation are not equivalent for this problem. Finally, we consider the case where the desired signal is also available at the helper. We develop new lower bounds for this setting that improve on those previously developed, and characterize the optimal distortion up to a constant multiplicative factor for some regimes of interest.

On secure source coding with side information at the encoder

We consider a secure source coding problem with side informations at the decoder and the eavesdropper. The encoder has a source that it wishes to describe with limited distortion through a rate-limited link to a legitimate decoder. The message sent is also observed by the eavesdropper. The encoder aims to minimize both the distortion incurred by the legitimate decoder; and the information leakage rate at the eavesdropper. When the encoder has access to the side information (S.I.) at the decoder, we characterize the rate-distortion-information leakage rate (R.D.I.) region under a Markov chain assumption and when S.I. at the encoder does not improve the rate-distortion region as compared to the case when S.I. is absent. We then extend our setting to consider the case where the encoder and decoder obtain coded S.I. through a rate-limited helper, and characterize the R.D.I. region for several special cases under logarithmic loss distortion (log-loss). Finally, we consider the case of list or entropy constraints at the decoder and show that the R.D.I. region coincides with R.D.I. region under log-loss.

A Note on the Broadcast Channel With Stale State Information at the Transmitter

This paper shows that the Maddah-Ali-Tse (MAT) scheme, which achieves the symmetric capacity of two example broadcast channels with strictly causal state information at the transmitter, is a simple special case of the Shayevitz-Wigger (SW) scheme for the broadcast channel with generalized feedback, which involves block Markov coding, Gray-Wyner compression, superposition coding, and Marton coding. Focusing on the class of symmetric broadcast channels with state, we derive an expression for the maximum achievable symmetric rate using the SW scheme. We show that the MAT results for the two-receiver case can be recovered by evaluating this expression for the special case in which superposition coding and Marton coding are not used. We then introduce a new broadcast channel example that shares many features of the MAT examples. We show that another special case of our maximum symmetric rate expression in which superposition coding is also used attains a higher symmetric rate than the MAT scheme. The symmetric capacity of this new example is not known, however.