We study the capacity region of a deterministic 4-node network, where 3 nodes can only communicate via the fourth one. However, the fourth node is not merely a relay since it can exchange private messages with all other nodes. This situation resembles the case where a base station relays messages between users and delivers messages between the backbone system and the users. We assume an asymmetric

A transmission scheme is developed for the downlink frame of cellular networks. While the mobile stations (MSs) maximize the signal power from the serving base station (BS), each BS aims at balancing the signal power of its users with the interference caused at the MSs of the neighboring cells, based on an approximated performance metric. A closed form solution for the beamforming vectors of the

This paper studies the performance of the Okumura-Hata model in the 900 MHz band. The results of several measurement campaigns carried out in different regions of Egypt show significant errors in the Okumura-Hata model. The paper, hence, introduces correction to the Okumura-Hata model that suits the Egyptian 900 MHz cellular environment. The correction is evaluated empirically by fitting the

In this paper, we analyze the performance of a secondary link in a cognitive radio (CR) system operating under statistical quality of service (QoS) delay constraints. In particular, we quantify analytically the performance improvement for the secondary user (SU) when applying a feedback based sensing scheme under the SINR Interference model. We leverage the concept of effective capacity (EC)

The two-way wiretap channel is considered in this paper. Two legitimate users, Alice and Bob, wish to exchange messages securely in the presence of a passive eavesdropper Eve. In the full-duplex scenario, where each node can transmit and receive simultaneously, new achievable secrecy rate regions are obtained based on the idea of allowing the two users to jointly optimize their channel prefixing

A cognitive multi-access network in which a primary user and a secondary user transmit to a common receiver is considered. The secondary user senses the channel at the beginning of each time slot to determine whether the primary user is active or idle. The sensing is not perfect; hence, the secondary user can miss the detection of an active primary user or erroneously declare an idle primary user

We investigate an ordered-access protocol for cognitive radios. The primary user (PU) operates in a time-slotted fashion and starts transmitting at the beginning of the time slot if its queue is nonempty. The secondary users, depending on their queues and spectrum sensing results, may start transmitting at times τ, 2τ , 3τ relative to the beginning of the time slot, where τ is the sensing duration

In this paper, we present a novel wideband multiple-input multiple-output Vehicle-to-Vehicle channel model. The proposed channel model is derived using the geometrical elliptical scattering approach. In order to emulate the appearance and disappearance of scatterers (vehicles, terrain, roadside units, etc.) in the environment, we associate a persistence process with each physical scatterer in the

A fundamental problem in cognitive radio systems is that the secondary user is ignorant of the primary channel state and the interference it inflicts on the primary license holder. We consider a secondary user that can eavesdrop on the ACK/NACK Automatic Repeat reQuest (ARQ) fed back from the primary receiver to the primary transmitter. Assuming the primary channel states follow a Markov chain

In this paper, we consider a time-slotted cognitive radio (CR) setting with buffered and energy harvesting primary and CR users. At the beginning of each time slot, the CR user probabilistically chooses the spectrum sensing duration from a predefined set. If the primary user (PU) is sensed to be inactive, the CR user accesses the channel immediately. The CR user optimizes the sensing duration