Soheil Gherekhloo

(Sub-)Optimality of Treating Interference as Noise in the Cellular Uplink With Weak Interference

Despite the simplicity of the scheme of treating interference as noise (TIN), it was shown to be sum-capacity optimal in the Gaussian interference channel (IC) with very-weak (noisy) interference. In this paper, the two-user IC is altered by introducing an additional transmitter that wants to communicate with one of the receivers of the IC. The resulting network thus consists of a point-to-point channel interfering with a multiple access channel (MAC) and is denoted by PIMAC. The sum-capacity of the PIMAC is studied with main focus on the optimality of TIN. It turns out that TIN in its naive variant, where all transmitters are active and both receivers use TIN for decoding, is not the best choice for the PIMAC. In fact, a scheme that combines both time division multiple access and TIN (TDMA–TIN) strictly outperforms the naive-TIN scheme. Furthermore, it is shown that in some regimes, TDMA–TIN achieves the sum-capacity for the deterministic PIMAC and the sum-capacity within a constant gap for the Gaussian PIMAC. In addition, it is shown that, even for very-weak interference, there are some regimes where a combination of interference alignment with power control and TIN at the receiver side outperforms TDMA–TIN. As a consequence, on the one hand, TIN in a cellular uplink is approximately optimal in certain regimes. On the other hand, those regimes cannot be simply described by the strength of interference.

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.

Resolving entanglements in topological interference management with alternating connectivity

The sum-capacity of a three user interference wired network for time-varying channels is considered. Due to the channel variations, it is assumed that the transmitters are only able to track the connectivity between the individual nodes, thus only the (alternating) state of the network is known. By considering a special subset of all possible states, we show that state splitting combined with joint encoding over the alternating states is required to achieve the sum-capacity. Regarding upper bounds, we use a genie aided approach to show the optimality of this scheme. This highlights that more involved transmit strategies are required for characterizing the degrees of freedom even if the transmitters have heavily restricted channel state information.

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.

Latency-Limited Broadcast Channel With Cache-Equipped Helpers

Decreasing communication latency is one of the main challenges for many applications in future communication systems. As a solution, we study in this work the benefits of using some cache-equipped helpers in a wireless communication scenario. More precisely, a wireless network with a transmitter, two cache-equipped helpers, and two receivers is studied from the latency point of view. While the transmitter has access to the whole data, the helpers store some data in their cache in order to support the transmitter in fulfilling the demands of the receivers. The main challenge is to develop a joint caching placement and the transmission strategy, which minimizes the latency of the communication. To this end, a general encoded caching is considered, in which each message is split into four types of sub-messages. The sub-messages of the first and second types are stored only in the cache of the first and second helper, respectively. The sub-messages of the third type are cached at both helpers, while the sub-messages of the fourth type are not cached at any helper. The size of the sub-messages is optimized in a way such that the delivery time of one bit for the worst-case demand is minimized. Moreover, a general lower bound on the delivery time is provided. Using this lower bound as a benchmark, the performance of the proposed caching policy is evaluated. It is shown that facilitating the cache-equipped helpers decreases the latency of broadcasting. Furthermore, it is shown that for the proposed caching policy, storing identical sub-messages in the cache of different helpers cannot be optimal if the cache size of the helpers is insufficiently large.

Extended generalized DoF optimality regime of treating interference as noise in the X channel

The simple scheme of treating interference as noise (TIN) is studied in this paper for the 3 × 2 X channel. A new sum-capacity upper bound is derived. This upper bound is transformed into a generalized degrees-of-freedom (GDoF) upper bound, and is shown to coincide with the achievable GDoF of a scheme that combines TDMA and TIN for some conditions on the channel parameters. These conditions specify a noisy interference regime which extends noisy interference regimes available in literature. As a by-product, the sum-capacity of the 3 × 2 X channel is characterized within a constant gap in the given noisy interference regime.

Coordination gains in the cellular uplink with noisy interference

This paper studies the performance gains of coordination in an elemental cellular network consisting of a multiple-access channel (MAC) and a point-to-point channel (P2P) interfering with each other. It is assumed that this network, denoted as PIMAC, is operating in the noisy (very-weak) interference regime. Three schemes, denoted as naive-TIN, TDMA-TIN, and IA-TIN, each with different coordination requirements among the transmitters (and receivers), are compared with each other in terms of achievable sum rates. It is shown that, although the PIMAC is in the noisy interference regime, allowing more coordination between the users might increase the performance, depending on the channel parameters. Consequently, this proves the sub-optimality of TDMA-TIN and naive-TIN in those regimes, which is in contrast to existing results for K-user interference and X channels. The analytical finding are verified by numerical evaluations.

On the optimality of treating interference as noise in the 2 × M LD X-channel

The optimality of the simple scheme of treating interference as noise (TIN) is studied in this paper for the 2 × M linear deterministic (LD) X-channel. A new capacity upper bound is derived. In the considered scheme (denoted as 2-IC-TIN), the setup is reduced to a 2-user interference channel while the receivers employ TIN. It is shown that as long as 2-IC-TIN is optimal in a M × 2 X-channel, it is also capacity-optimal in the 2 × M X-channel which is generated by changing the role of transmitters and receivers. The result of this paper expands the capacity optimal regime of TIN for the 2 × M LD X-channel compared to the state of the art.

Optimal Power Splitting for Simultaneous Information Detection and Energy Harvesting

This letter deals with the joint information and energy processing at the receiver of a point-to-point communication channel. In particular, the tradeoff between the achievable information rate and harvested energy for a multiple-antenna power splitting receiver is investigated. Here, the rate-energy region characterization is of particular interest, which is intrinsically a nonconvex problem. In this letter, an efficient algorithm is proposed for obtaining an approximate solution to the problem in polynomial time. This algorithm is mainly based on the Taylor approximation in conjunction with semidefinite relaxation, which is solved by interior-point methods. Moreover, we utilize the Gaussian randomization procedure to obtain a feasible solution for the original problem. It is shown that by proper receiver design the rate-energy region can be significantly enlarged compared to the state of the art, while at the same time the receiver hardware costs is reduced by utilizing less number of energy harvesting circuitry.

The Information-Theoretic Constant-Gap Optimality of Treating Interference as Noise in Interference Networks

Treating interference as noise is one of the simplest methods for the management of interference in wireless networks. Despite its simplicity, treating interference as noise (TIN) was shown to be information-theoretically optimal for certain Gaussian interference channels (IC) with very-weak (noisy) interference. In this chapter, we consider cellular networks, such as networks that consists of a point-to-point channel interfering with a multiple access channel (MAC). The sum-capacity of such networks is studied with main focus on the constant-gap optimality of TIN rather than on its exact optimality. It turns out that TIN in its naive variant, where all transmitters are active and receivers use TIN for decoding, is not the best choice for certain networks. In fact, a scheme that combines both time division multiple access and TIN (TDMA-TIN) strictly outperforms the naive TIN scheme. Furthermore, it is shown that in some regimes, TDMA-TIN achieves the sum-capacity within a constant gap for Gaussian networks. Additionally, it is shown that, even for very-weak interference, there are some regimes where a combination of interference alignment with power control and treating interference as noise at the receiver side outperforms TDMA-TIN. As a consequence, on the one hand treating interference as noise in a cellular uplink is approximately optimal in certain regimes. On the other hand, those regimes cannot be simply described by the strength of interference, requiring a careful design of wireless networks.