This paper investigates the effect of cognitive operations in the physical (PHY) layer on the throughput of the transport layer in Cognitive Mobile Ad Hoc Networks (CoMANETs). The focus is on the use of soft sensing to enhance secondary users capacity in the PHY layer. A new transport layer protocol is proposed which updates the Congestion Window (CW) efficiently according to the power and rate adaptation strategy of the soft sensing scheme. The expected throughput is derived and compared to the case where the transport layer is oblivious to the use of soft sensing, as well as to a benchmark case from the literature where only hard sensing is used. Results show significant throughput improvements due to soft sensing in general. These improvements increase with proper adaptation of the transport layer protocol.

This paper investigates the weighted sum degrees of freedom (DoF) of the MIMO Y channel that consists of three users, where the j-th user is equipped with Mjantennas, and a relay equipped with N antennas. In this network, each user conveys two private messages to the other two users in addition to a common message directed to both of them. As there is no direct link between the users, communication occurs through the relay. We define a weighted sum DoF metric that integrates all the network messages and weights the common message by a factor of α. Then, we study the weighted sum DoF maximization problem for α ≥ 0. Specifically, we show that the weighted sum DoF of the network, with M1≥ M2≥ M3, is given by min{2N, 2M2+ 2M3, M1+ M2+ M3}, for 0 ≤ α ≤ 4/3. While, for 4/33) + 3α/2 M3, 2(2N - M2- M3) + 3α/2 (M2+ M3- N), (6N - 2(M1+ M2+M3))+ 3α/2 (M1+ M2+ M3-2N), 2M2+ 2M3, M1+ M2+ M3}, and finally, for α > 2, the weighted sum DoF is equal to min{3α/2 N, α/2 (2N + M3), 2(N - 3/2M3) + 2αM3, α/2 (N + M2+ M3), N + M2- 3M3+ 2αM3, α/2 (M1+ M2+ M3), M1+ M2- 3M3+ 2αM3, 2(M2- M3) + 2αM3}. Achievability of the sum DoF is shown by using signal space alignment for network coding in the uplink phase, and zero-forcing precoding in the downlink phase.

In this paper, we characterize the total degrees of freedom (DoFs) of the full-duplex asymmetric multiple-input multiple- output (MIMO) three-way channel. Each node has a separate-antenna full-duplex MIMO transceiver with a different number of antennas, where each antenna can be configured for either signal transmission or reception. We study this system under two message configurations; the first configuration is when each node has two unicast messages to be delivered to the two other nodes, while the second configuration is when each node has two unicast messages as well as one broadcast message to be delivered to the two other nodes. For each configuration, we first derive upper bounds on the total DoF of the system. Cut-set bounds in conjunction with genie-aided bounds are derived to characterize the achievable total DoF. Afterward, we analytically derive the optimal number of transmit and receive antennas at each node to maximize the total DoF of the system, subject to the total number of antennas at each node. Finally, the achievable schemes for each configuration are constructed. The proposed schemes are mainly based on zero-forcing and null-space transmit beamforming. We show that the derived outer and inner bounds on the total DoF are tight for each message configuration.

In this paper, we study the general multiple input multiple output (MIMO) multi-way relay channel, i.e., MIMO Y channel, with common and private messages. In this channel, K users exchange messages through a common relay. Each user transmits a private message to each user in addition to a common message to all the other users. The ith user and the relay are equipped with Miand N antennas, respectively. First, we derive the degrees of freedom (DoF) region of the symmetric three-user MIMO Y channel, where Mi= M and i ∈ (1,2,31. Due to the symmetry of the network, we focus on the case where the DoF of all private messages are equal and the DoF of all common messages are equal. In this case, the DoF region has two dimensions: the DoF of private messages and the DoF of common messages. We develop an outer bound on the DoF region based by using cut-set and one-sided genie bounds. We prove the achievability of the outer bound on the DoF region by using linear beamforming and signal space alignment (SSA) schemes. Second, based on our study of the DoF region of the symmetric channel, we define a weighted sum DoF metric that integrates all the network messages and weights the common messages by a factor of α. We study the weighted sum DoF maximization problem and show that sending common messages only is optimal when α exceeds 43. Next, we focus on the weighted sum DoF with α = 2 that represents the total number of received interference-free streams at the users. First, we show that the weighted sum DoF, with α = 2, of the MIMO Y channel with an arbitrary number of antennas is given by min(3N, 2N + M3, N + M2+ M3, 2M2+ 2M3, M1+ M2+ M3). Second, we study the weighted sum DoF, with α = 2, of the K-user case in the symmetric setting. We derive an outer bound on the weighted sum DoF using cut-set bounds, and show that the network has K min(N, M) weighted DoF. The achievability results are obtained by using SSA for network coding in the multiple access phase, and zero-forcing precoding in the broadcast phase.

In this paper, we characterize the asymmetric total degrees of freedom (DoF) of a multiple-input multiple-output (MIMO) 3-way channel. Each node has a separate-antenna full-duplex MIMO transceiver with a different number of antennas, where each antenna can be configured for either signal transmission or reception. Each node has two unicast messages to be delivered to the two other nodes. We first derive upper bounds on the total DoF of the system. Cut-set bounds in conjunction with genie-aided bounds are derived to characterize the achievable total DoF. Afterwards, we analytically derive the optimal number of transmit and receive antennas at each node to maximize the total DoF of the system, subject to the total number of antennas at each node. Finally, the achievable schemes are constructed. The proposed schemes are mainly based on zero-forcing and null-space transmit beamforming.

Abstract In this paper, we derive the capacity of the deterministic relay networks with relay messages. We consider a network that consists of five nodes, four of which can only communicate via the fifth one. However, the fifth node is not merely a relay as it may exchange private messages with the other network nodes. First, we develop an upper bound on the capacity region based on the notion of a single‐sided genie. In the course of the achievability proof, we also derive the deterministic capacity of a four‐user relay network (without private messages at the relay). The capacity achieving schemes use a combination of two network coding techniques: the simple ordering scheme and detour scheme. In the simple ordering scheme, we order the transmitted bits at each user such that the bi‐directional messages will be received at the same channel level at the relay, while the basic idea behind the detour scheme is that some parts of the message follow an indirect paths to their respective destinations. This paper, therefore, serves to show that user cooperation and network coding can enhance throughput, even when the users are not directly connected to each other. Finally, we make a conjecture about the capacity region of the generalK‐node relay network with relay messages. Copyright © 2016 John Wiley & Sons, Ltd.

We investigate the degrees of freedom (DoF) of the downlink of a cellular relay network. In this network, two base stations transmit to two mobile stations via relays due to the absence of a direct communication link. Each base station and mobile station is equipped with $M$ antennas. Each base station has two messages; one to each mobile station, and uses two relays to transmit to the mobile stations. The relays are half duplex, decode-and-forward and equipped with $N$ antennas each. We consider two configurations of the relays; shared and dedicated relays. In the shared relays configuration, the system has two relays that are used by both base stations. Whereas, in the dedicated relays configuration, each base station has two dedicated relays, i.e., the system has four relays. We consider all possible relaying schemes where the base stations can use the relays either simultaneously or alternately. We derive an upper bound on the DoF achievable by each relaying scheme as a function of the ratio between $N$ and $M$. Furthermore, we propose an achievable scheme that uses interference alignment to achieve the upper bound on the DoF for the shared relays configuration, and for all values of $M$ and $N$ except for $1<;\frac{N}{M}<;\frac{5}{2}$ in the dedicated relays configuration.

In this paper we investigate the degrees of freedom of a cellular relay network that consists of two base stations, two mobile stations and four decode-and-forward relays. The base stations and the mobile stations are equipped with M antennas each, whereas the relays are equipped with N antennas each. In addition, each base station has an independent message to each mobile station. The relays are used to froward the messages from the base stations to the mobile station as there is no direct link. We consider three different relaying architectures where the two relays associated with each base station simultaneously or alternately transmit their messages. We derive an upper bound on the degrees of freedom achievable by each relaying architecture as a function of the ratio between N and M. Furthermore, we propose an achievable scheme that uses interference alignment to achieve the upper bound on the DoF for all values of M and N except for 1 ≤ N/M ≤ 5/2.

In this paper, we study the degrees of freedom (DoF) of the MIMO relay networks. We start with a general Y channel, where each user has Miantennas and aims to exchange messages with the other two users via a relay equipped with N antennas. Then, we extend our work to a general 4-user MIMO relay network. Unlike most previous work which focused on the total DoF of the network, our aim here is to characterize the achievable DoF region as well. We develop an outer bound on the DoF region based on the notion of one sided genie. Then, we define a new achievable region using the Signal Space Alignment (SSA) and the Detour Schemes. Our achievable scheme achieves the upper bound for certain conditions relating Mi's and N.

In this paper, a platform for measuring the impulse response of wireless multiple-input-multiple-output (MIMO) vehicle-to-vehicle (V2V) channels is presented. The platform is developed using Rice University Wireless Open-Access Research Platform (WARP) boards and utilized to perform an experimental study of V2V channels through conducting field measurements. A full characterization of MIMO-V2V channels is given via extracting the channel parameters from the acquired measurements. These parameters include the power-delay profile, the Doppler spectrum, and the MIMO transmit and receive correlation matrices of the channel. Numerical simulations are utilized to examine the effect of the channel parameters on the bit error rate (BER) performance of an orthogonal frequency division multiplexing (OFDM) based system.

In this paper, we completely characterize the deterministic capacity region of a four-node relay network with no direct links between the nodes, where each node communicates with the three other nodes via a relay. Towards this end, we develop an upper bound on the deterministic capacity region, based on the notion of a one-sided genie. To establish achievability, we use the detour schemes that achieve the upper bound by routing specific bits via indirect paths instead of sending them directly.

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 scenario where the channel between any two nodes is not reciprocal. First, an upper bound on the capacity region is obtained based on the notion of single sided genie. Subsequently, we construct an achievable scheme that achieves this upper bound using a superposition of broadcasting node 4 messages and an achievable “detour” scheme for a reduced 3-user relay network.

Space frequency block coding with orthogonal frequency division multiplexing (SFBC-OFDM) suffers from the effect of inter-carrier interference (ICI) in doubly-selective communication channels. In this paper, a scheme is proposed in which windowing is applied to the received signal to reduce the effect of ICI to a limited number of neighboring sub-carriers. The sub-carriers holding the SFBC components of each codeword are separated by a number of sub-carriers larger than the ICI range, and hence, they do not interfere with each other. In order to preserve the structure of the SFBC, the separation between the codeword components is also selected within the coherence bandwidth of the channel. As a result, the diversity gain of the SFBC is preserved. A decision feedback equalizer is proposed to estimate the transmitted data symbols with low complexity. Simulation results are presented showing the ability of the proposed scheme to significantly improve the performance of SFBC-OFDM and preserve its diversity gain.

In this paper, we completely characterize the deterministic multicast capacity region of the symmetric two-pair bidirectional half duplex relay network with private messages. Towards this end, we first develop a new upper bound on the deterministic capacity region, based on the notion of a one-sided genie. We then proceed to construct novel detour schemes that achieve the upper bound by routing the bits intended for a certain receiver through the network rather than sending it directly. To the best of the authors' knowledge, this scenario corresponds to one of the rare cases where coding, across levels and time, is needed to achieve the deterministic capacity of the network.

This paper considers an interference network composed of K half-duplex single-antenna pairs of users who wish to establish bi-directional communication with the aid of a multi-input-multi-output (MIMO) half-duplex relay node. This channel is referred to as the ¿MIMO wireless switch¿ since, for the sake of simplicity, our model assumes no direct link between the two end nodes of each pair implying that all communication must go through the relay node (i.e., the MIMO switch). Assuming a delay-limited scenario, the fundamental limits in the high signal-to-noise ratio (SNR) regime is analyzed using the diversity-multiplexing tradeoff (DMT) framework. Our results sheds light on the structure of optimal transmission schemes and the gain offered by the relay node in two distinct cases, namely reciprocal and non-reciprocal channels (between the relay and end-users). In particular, the existence of a relay node, equipped with a sufficient number of antennas, is shown to increase the multiplexing gain; as compared with the traditional fully connected K-pair interference channel. To the best of our knowledge, this is the first known example where adding a relay node results in enlarging the pre-log factor of the sum rate. Moreover, for the case of reciprocal channels, it is shown that, when the relay has a number of antennas at least equal to the sum of antennas of all the users, static time allocation of decode and forward (DF) type schemes is optimal. On the other hand, in the non-reciprocal scenario, we establish the optimality of dynamic decode and forward in certain relevant scenarios.

In this correspondence, a new bound on the performance of multiuser receivers in fading channels is presented. The bound is based on a novel criterion for decomposability of error sequences. A constructive method to find the set of indecomposable error sequences under the new criterion is presented. Although the presentation is in the context of a narrow-band multiuser system, the improved bounds can be applied directly to code-division multiple-access (CDMA) multiuser systems over flat-fading channels. A modified bound is also developed for multipath-fading channels. Several examples demonstrate the improved tightness of the new bound, relative to previous results

In this paper, we study the effect of the scattering environment on the capacity of a single carrier linear modulation used in a multipath, multiple antenna channel. The work incorporates detailed 3D geometric channel models to assess the effect of spatial correlation. The analysis techniques, based on the pioneering work of Hirt and Massey (1988), provide a method to evaluate outage capacity. Channels that are derivatives of the ETSI standard hilly terrain and typical urban are considered in detail. The results quantify the loss of capacity produced by higher spatial correlation. When comparing signals of different bandwidth, wideband systems produce more diversity due to better temporal resolution. Surprisingly, narrowband systems gain some diversity back by being less susceptible to loss of diversity from spatial correlation

A three-dimensional model is proposed for simulating the wireless channel. The model allows simulation of the effects of realistic channels on space-time processing and coding systems. The model is characterized by a set of scattering centers with a given mean angle of arrival (departure), angle spread (azimuth and elevation), and propagation delay. Additionally, the model accommodates either transmitter or receiver motion. Spatial characteristics of the simulated channels match previously obtained analytical results. We use the model to generate standardized temporal and spatial channel conditions from Global System for Mobile communication and third-generation standards. We demonstrate the need for such a spatial description by contrasting our results to classic methods of generating these standardized channel conditions.

A new bound on the performance of multiuser receivers in fading channels is presented. The bound is based on a novel criterion for decomposability of error sequences. Although the bound development is in the context of a narrowband multiuser system, the improved bounds can be applied directly to CDMA multiuser systems over a fading channels. Several examples demonstrate the tightness of the new bound, relative to previous results from the literature.

A three dimensional model is proposed for simulating the wireless channel. The model allows simulation of the effects of realistic channels on space-time processing and coding systems. The model is characterized by a set of scattering centers with a given mean angle of arrival (departure), angle spread (azimuth and elevation) and propagation delay. Additionally the model accommodates either transmitter or receiver motion. Several examples are considered and the simulation characteristics match the previously obtained analytical model results.