Zohaib Hassan Awan

Multiaccess Channel With Partially Cooperating Encoders and Security Constraints

We study a special case of Willemss two-user multiaccess channel with partially cooperating encoders from a security perspective. This model differs from Willemss setup in that 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 based on a combination of Willemss coding scheme, noise injection, 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 show that, under certain conditions, these bounds agree in some extreme cases of cooperation between the encoders. We illustrate our results through some numerical examples.

Secure Communication Over Parallel Relay Channel

We investigate the problem of secure communication over parallel relay channel in the presence of a passive eavesdropper. We consider a four-terminal relay-eavesdropper channel which consists of multiple relay-eavesdropper channels as subchannels. For the discrete memoryless model, we establish outer and inner bounds on the rate-equivocation region. The inner bound allows mode selection at the relay. For each subchannel, secure transmission is obtained through one of two coding schemes at the relay: decoding-and-forwarding the source message or confusing the eavesdropper through noise injection. For the Gaussian memoryless channel, we establish lower and upper bounds on the perfect secrecy rate. Furthermore, we study a special case in which the relay does not hear the source and show that under certain conditions the lower and upper bounds coincide. The results established for the parallel Gaussian relay-eavesdropper channel are then applied to study the fading relay-eavesdropper channel. Analytical results are illustrated through some numerical examples.

Secure Degrees of Freedom of MIMO X-Channels With Output Feedback and Delayed CSIT

We investigate the problem of secure transmission over a two-user multi-input multi-output (MIMO) X-channel with noiseless local feedback and delayed channel state information (CSI) available at transmitters. The transmitters are equipped with M antennas each, and the receivers are equipped with N antennas each. For this model, we characterize the optimal sum secure degrees of freedom (SDoF) region. We show that, in presence of local feedback and delayed CSI, the sum SDoF region of the MIMO X-channel is same as the SDoF region of a two-user MIMO BC with 2M antennas at the transmitter and N antennas at each receiver. This result shows that, upon availability of feedback and delayed CSI, there is no performance loss in sum SDoF due to the distributed nature of the transmitters. Next, we show that this result also holds if only global feedback is conveyed to the transmitters. We also study the case in which only local feedback is provided to the transmitters, i.e., without CSI, and derive a lower bound on the sum SDoF for this model. Furthermore, we specialize our results to the case in which there are no security constraints. In particular, similar to the setting with security constraints, we show that the optimal sum degrees of freedom (sum DoF) region of the (M, M, N, N)-MIMO X-channel is same of the DoF region of a two-user MIMO BC with 2M antennas at the transmitter and N antennas at each receiver. We illustrate our results with some numerical examples.

Fundamental limits of caching in D2D networks with secure delivery

We study the problem of secure transmission over a caching D2D network. In this model, end users can prefetch a part of popular contents in their local cache. Users make arbitrary requests from the library of available files and interact with each other to deliver requested contents from the local cache to jointly satisfy their demands. The transmission between the users is wiretapped by an external eavesdropper from whom the communication needs to be kept secret. For this model, by exploiting the flexibility offered by the local cache storage, we establish a coding scheme that not only conforms to the demands of all users but also delivers the contents securely. In comparison to the insecure caching schemes, the coding scheme that we develop in this work illustrates that for large number of files and users, the loss incurred due to the imposed secrecy constraints is insignificant. We illustrate our result with the help of some examples.

Fundamental limits on latency in cloud- and cache-aided HetNets

Hybrid architectures are generally composed of a cyber cloud with additional support of edge caching. By utilizing the benefits associated with cloud computing and caching, powerful enhanced interference management techniques can be readily utilized — that among others — also results in low-latency transmission. In this paper, we study the impact of cloud and edge processing on the latency for a heterogenous network (HetNet) consisting of two users and two transmitters. We define an information-theoretic metric, the delivery time per bit (DTB), that captures the delivery latency. We establish bounds on the DTB as a function of cache size, backhaul capacity and wireless channel parameters. We show the optimality on the DTB for various channel regimes.

Achievable secure degrees of freedom of MISO broadcast channel With alternating CSIT

We study the problem of secure transmission over a two-user Gaussian multi-input single-output (MISO) broadcast channel under the assumption that the channel to each receiver is conveyed either perfectly (P) or with delay (D) to the transmitter. Denoting S₁ and S₂ to be the channel state information at the transmitter (CSIT) of user 1 and user 2, respectively; the overall CSIT can then alternate between four states, i.e., (S₁, S₂) ∈ {P,D}². We denote λ_S1S2 be the fraction of time the state S₁S₂ occurs, and focus on the symmetric case such that λ_S1S2 = λ_S2S1. Under these assumptions, we first consider the Gaussian MISO wiretap channel and characterize the secure degrees of freedom (SDoF). Next, we generalize this model to the two-user Gaussian MISO broadcast channel and establish an inner bound on the SDoF region. This result shows the synergistic SDoF gains of alternating CSIT and illustrates that, as opposed to encoding separately over different states, an improved SDoF region is achievable by joint encoding across these states.

On multiaccess channel with unidirectional cooperation and security constraints

We study a special case of Willemss two-user multi-access channel with partially cooperating encoders from a security perspective. This model differs from Willemss 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 Willemss 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.

On SDoF of Multi-Receiver Wiretap Channel With Alternating CSIT

We study the problem of secure transmission over a Gaussian multi-input single-output (MISO) two receiver channel with an external eavesdropper, under the assumption that the state of the channel which is available to each receiver is conveyed either perfectly (

On secure transmission over parallel relay eavesdropper channel

P

Secure degrees of freedom of MIMO X-channels with output feedback and delayed CSI

) or with delay (