Jaber Kakar

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.

Analysis and Mitigation of Interference to the LTE Physical Control Format Indicator Channel

In LTE, the Physical Control Format Indicator Channel (PCFICH) is a downlink control channel that indicates the number of OFDM symbols used by the primary downlink control channel in each sub frame. Even though the PCFICH only carries two bits of control information, it is essential to the operation of LTE. Since the PCFICH is a vital physical channel that only occupies a small fraction of the downlink signal, it acts as a weak link in terms of vulnerability to targeted interference. Due to recent interest in using LTE for military and public safety applications, it would be beneficial to better understand this vulnerability. This paper investigates the performance of the PCFICH under various harsh wireless conditions and proposes strategies to prevent interference against the PCFICH from causing link degradation.

Fundamental limits on latency in transceiver cache-aided HetNets

Stringent mobile usage characteristics force wireless networks to undergo a paradigm shift from conventional connection-centric to content-centric deployment. With respect to 5G, caching and heterogenous networks (HetNet) are key technologies that will facilitate the evolution of highly content-centric networks by facilitating unified quality of service in terms of low-latency communication. In this paper, we study the impact of transceiver caching on the latency for a HetNet consisting of a single user, a receiver and one cache-assisted transceiver. We define an information-theoretic metric, the delivery time per bit (DTB), that captures the delivery latency. We establish coinciding lower and upper bounds on the DTB as a function of cache size and wireless channel parameters; thus, enabling a complete characterization of the DTB optimality of the network under study. As a result, we identify cache beneficial and non-beneficial channel regimes.

A Survey on Robust Interference Management in Wireless Networks

Recent advances in the characterization of fundamental limits on interference management in wireless networks and the discovery of new communication schemes on how to handle interference led to a better understanding towards the capacity of such networks. The benefits in terms of achievable rates of powerful schemes handling interference, such as interference alignment, are substantial. However, the main issue behind most of these results is the assumption of perfect channel state information at the transmitters (CSIT). In the absence of channel knowledge the performance of various interference networks collapses to what is achievable by time division multiple access (TDMA). Robustinterference management techniques are promising solutions to maintain high achievable rates at various levels of CSIT, ranging from delayed to imperfect CSIT. In this survey, we outline and study two main research perspectives of how to robustly handle interference for cases where CSIT is imprecise on examples for non-distributed and distributed networks, namely broadcast and X-channel. To quantify the performance of these schemes, we use the well-known (generalized) degrees of freedom (GDoF) metric as the pre-log factor of achievable rates. These perspectives maintain the capacity benefits at similar levels as for perfect channel knowledge. These two perspectives are: First,scheme-adaptationthat explicitly accounts for the level of channel knowledge and, second,relay-aided infrastructure enlargementto decrease channel knowledge dependency. The relaxation on CSIT requirements through these perspectives will ultimately lead to practical realizations of robust interference management techniques. The survey concludes with a discussion of open problems.

Achieving the optimal DoF with feedback and mixed CSIT for the 3×2 X-channel.

There is an increasing demand of robust interference management methods which provide strong performance even when channel state information is imperfect. To investigate this aspect, we study the 3 × 2 single-input single-output (SISO) X-channel where each transmitter wants to send an independent message to each receiver. We assume that each receiver is allowed to convey perfect outdated and imperfect instantaneous channel state information to the transmitter (CSIT). Furthermore a single transmitter-receiver pair exists that allows for output feedback. For this model, we establish a lower bound on the sum degrees-of-freedom (DoF) by introducing a new achievability scheme. We show that, finite quality CSIT and partial output feedback together compensate for the absence of perfect CSIT.