Maximum Achievable Rate Research Articles

Active sequential hypothesis testing

Consider a decision maker who is responsible to dynamically collect observations so as to enhance his information about an underlying phenomena of interest in a speedy manner while accounting for the penalty of wrong declaration. Due to the sequential nature of the problem, the decision maker relies on his current information state to adaptively select the most ``informative'' sensing action among the available ones. In this paper, using results in dynamic programming, lower bounds for the optimal total cost are established. The lower bounds characterize the fundamental limits on the maximum achievable information acquisition rate and the optimal reliability. Moreover, upper bounds are obtained via an analysis of two heuristic policies for dynamic selection of actions. It is shown that the first proposed heuristic achieves asymptotic optimality, where the notion of asymptotic optimality, due to Chernoff, implies that the relative difference between the total cost achieved by the proposed policy and the optimal total cost approaches zero as the penalty of wrong declaration (hence the number of collected samples) increases. The second heuristic is shown to achieve asymptotic optimality only in a limited setting such as the problem of a noisy dynamic search. However, by considering the dependency on the number of hypotheses, under a technical condition, this second heuristic is shown to achieve a nonzero information acquisition rate, establishing a lower bound for the maximum achievable rate and error exponent. In the case of a noisy dynamic search with size-independent noise, the obtained nonzero rate and error exponent are shown to be maximum.

Unicast Multi-Antenna Relay Beamforming With Per-Antenna Power Control: Optimization and Duality

We consider amplify-and-forward multi-antenna relaying between a single pair of source and destination under relay per-antenna power constraints. We design the optimal relay processing matrix to minimize the maximum per-antenna power budget for a received SNR target. With given transmit and receive beamformers at the source and destination, respectively, we first focus on the equivalent system with single-antenna source and destination. Although non-convex, we show that the optimization satisfies strong Lagrange duality and can be solved in the Lagrangian dual domain. We reveal a prominent structure of this problem, by establishing its duality with direct SIMO beamforming system with an uncertain noise. This enables us to derive a semi-closed form expression for the optimal relay processing matrix that depends on a set of dual variables, which can be determined through numerical optimization with a significantly reduced problem space. We further show that the dual problem has a semi-definite programming form, which enables efficient numerical optimization methods to determine the dual variables with polynomial complexity. Using this result, the reverse problem of SNR maximization under a set of relay per-antenna power constraints is then addressed. We then consider the maximum relay beamforming achievable rate under different combinations of antenna setups at source and destination. In particular, we generalize the duality to MIMO relay beamforming vs. direct MIMO beamforming, and establish the dual relation of the two systems for different multi-antenna setups at source and destination.

Multi-Step FRET-Based Long-Range Nanoscale Communication Channel

Nanoscale communication based on Forster Resonance Energy Transfer (FRET) is a promising paradigm that allows future molecular-size machines to communicate with each other over distances up to 10 nm using the excited state energies of fluorescent molecules. In this study, we propose a novel nanoscale communication method based on multi-step FRET using identical fluorophores as relay nodes between communicating nanomachines, and utilizing multi-exciton transmission scheme in order to improve the limited range of the communication and achievable transmission rate over the nanoscale channel. We investigate two communication scenarios: immobile nanomachines communicating through a channel in a host material with linearly located relay nodes, and mobile nanomachines communicating through a channel in a 3-dimensional aqueous environment with randomly deployed relay nodes. We simulate the communication over these channels with realistic algorithms considering the high degree of randomness intrinsic to FRET phenomenon. Using the simulation results and following a Monte Carlo approach, we evaluate the performance of the channels by means of information theoretical capacity and interference probability. We show that multi-step FRET-based communication significantly outperforms the other biologically inspired nanocommunication techniques proposed so far in terms of maximum achievable data transmission rates. The results underline the compatibility and practicality of the FRET-based communication for several applications ranging from molecular computers to nanosensor networks.

Uplink resource allocation in OFDMA system using distributed antennas

In this article, we investigate uplink resource allocation in orthogonal frequency division multiple access (OFDMA) systems that use distributed antennas. The multiple distributed receiving antennas motivate us to exploit the spatial diversity to maximize the achievable rate of the system. Given constraints on the subcarrier allocation and the power limit of each user equipment (UE), a mixed-integer optimization problem is formulated. We first propose a centralized greedy algorithm to find the maximum achievable rate of the system. Then a heuristic algorithm is proposed that can be implemented in a distributed manner. Simulation results show that the heuristic algorithm can approximately achieve the maximum achievable rate of the system and result in significant system performance improvement over the approach assigning one user to each subcarrier.

Analysis of the Uplink Maximum Achievable Rate With Location-Dependent Intercell Signal Interference Factors Based on Linear Wyner Model

To enhance spectral efficiency, full frequency reuse has been adopted in advanced cellular communication networks, which, however, generates severe intercell cochannel interference and degrades the achievable rate at mobile terminals, particularly for those located near cell boundaries. Therefore, it is of great importance and interest for network operators and service providers to evaluate and understand the impact of locationdependent intercell cochannel interference on the achievable data rate in cellular networks. In this paper, considering a realistic spatial distribution of user locations, we first derive and analyze the probability density function (pdf) of the intercell power interference factor, which represents path loss of the adjacent cell signals, for the classic linear Wyner model. The closed-form result of the maximum achievable rate in cellular uplink channels is also derived under the Nakagami- m fading model. Based on these new results, an upper bound of the uplink maximum achievable rate with location-dependent intercell signal interference factors is calculated. Furthermore, the rate is analyzed in a running-train scenario for the application of the linear Wyner model. Numerical results show that user locations have strong impact on the maximum achievable rate per cell.

Esense: Energy Sensing-Based Cross-Technology Communication

In this paper, we present Esense, a new paradigm of communication between devices that have fundamentally different physical layers. Esense is based on sensing and interpreting energy profiles. While our ideas are generic enough to be applicable in a variety of contexts, we illustrate the usefulness of our ideas by presenting novel solutions to existing problems in three distinct research domains. As part of these solutions, we demonstrate the ability to communicate between devices that follow two different standards: IEEE 802.11 and 802.15.4. We consider two scenarios here: 1) where there is no background traffic and 2) where there is background 802.11 traffic. In each case, we build an seta: a set of signature packet sizes that can be used for Esense communication. Specifically for the second case, we take a measurement-based alphabet set construction by considering WiFi traces from actual deployments. Based on practical observations and experiments, we theoretically quantify the maximum achievable transmission rate when using Esense. With background traffic, we could potentially construct an alphabet of size as high as 100. Such a large alphabet size promises efficient Esense communication. We show via a prototype implementation that effective communication is indeed feasible even when both sides use different physical layers.

Secure Beamforming via Amplify-and-Forward Relays in Machine-to-Machine Communications

We consider the collaborative use of amplify-and-forward relays to form a beamforming system and provide physical layer security for a wireless machine-to-machine (M2M) communication network. We investigate two objectives: (i) the achievable secrecy rate maximization subject to the relay power constraint and (ii) the relay transmit power minimization under a secrecy rate constraint. For the first objective, we propose a secrecy rate maximization (SRM) beamforming scheme. The secrecy rate maximization problem can be formed into a two-level optimization problem and we solve it using semidefinite relaxation (SDR) techniques. To reduce the complexity of the SRM beamforming scheme, a virtual eavesdropper-based SRM (VE-SRM) beamforming scheme is proposed, in which we hypothesize a virtual eavesdropper instead of all eavesdroppers and maximize the secrecy rate according to the virtual eavesdropper. In addition, for the second objective, we design a relay power minimization (RPM) beamforming scheme, in which an iterative algorithm combining the SDR technology and the gradient-based method is devised by studying the convexity of the RPM problem. By relaxing the constraints of the RPM beamforming scheme, we propose a virtual eavesdropper-based RPM (VERPM) beamforming scheme, which reduces the multivariate RPM problem to a problem of a single variable, and thus an analytical solution is obtained. Our proposed beamforming designs can work well even if the number of eavesdroppers is larger than that of relays, while the existing schemes, for example, the null-space beamforming schemes, cannot work under this condition. Simulation results are presented to demonstrate the significance of performance improvements with the SRM and RPM beamforming schemes. It is also shown that the virtual eavesdropper approaches significantly reduce the complexity with acceptable performance degradation.

Achievable rates optimization for broadcast channels using finite size constellations under transmission constraints

Abstract In this paper, maximal achievable rate regions are derived for power-constrained AWGN broadcast channel involving finite constellations and two users. The achievable rate region is studied for various transmission strategies including superposition coding and compared to standard schemes such as time sharing. The maximal achievable rates are obtained by optimizing over both the joint distribution of probability and over the constellation symbol positions. A numerical solution is proposed for solving this non-convex optimization problem. Then, we consider several variations of the same problem by introducing various constraints on the optimization variables. The aim is to evaluate efficiency vs. complexity tradeoffs of several transmission strategies, some of which (the simplest ones) can be found in actual standards. The improvement for each scheme is evaluated in terms of SNR savings for target achievable rates or/and percentage of gain in achievable rates for one user compared to a reference scheme. As an application, two scenarios of coverage areas and user alphabets are considered. This study allows to evaluate with practical criteria the performance improvement brought by more advanced schemes.

Downlink Scheduling and Resource Allocation for Cognitive Radio MIMO Networks

Cognitive radio is regarded as the ideal candidate for enhancing the efficiency of spectrum usage for next-generation wireless systems. In fact, this emerging technology allows unlicensed cognitive users to transmit over frequency bands that are initially owned by license holders through the use of dynamic spectrum sharing. In this paper, we propose a novel algorithm that efficiently solves the problem of spectrum sharing and user scheduling in a cognitive downlink multi-input-multi-output system (MIMO). We study the scenario where primary receivers do not allow any interference from a multiantenna cognitive base station, which serves cognitive users. Using graph theory, we model, formulate, and develop an algorithm that finds near-optimal spectrum sharing with the objective of approaching the maximum achievable secondary sum rate. Since the formulated graph-coloring problem is shown to be NP-hard, we design a low-complexity greedy algorithm. Following, we add the well-known proportional fairness to the proposed algorithm to ensure time-based fairness and to efficiently resolve the fairness/sum rate tradeoff. The problem is also formulated as a binary integer programming problem to find the optimal coloring solution. Computer simulations show that the proposed algorithm is able to achieve near-optimal performances with low computational complexity.

A 1.5 ns OFF/ON Switching-Time Voltage-Mode LVDS Driver/Receiver Pair for Asynchronous AER Bit-Serial Chip Grid Links With Up to 40 Times Event-Rate Dependent Power Savings

This paper presents a low power fast ON/OFF switchable voltage mode implementation of a driver/receiver pair intended to be used in high speed bit-serial Low Voltage Differential Signaling (LVDS) Address Event Representation (AER) chip grids, where short (like 32-bit) sparse data packages are transmitted. Voltage-Mode drivers require intrinsically half the power of their Current-Mode counterparts and do not require Common-Mode Voltage Control. However, for fast ON/OFF switching a special high-speed voltage regulator is required which needs to be kept ON during data pauses, and hence its power consumption must be minimized, resulting in tight design constraints. A proof-of-concept chip test prototype has been designed and fabricated in low-cost standard 0.35 μ m CMOS. At ± 500 mV voltage swing with 500 Mbps serial bit rate and 32 bit events, current consumption scales from 15.9 mA (7.7 mA for the driver and 8.2 mA for the receiver) at 10 Mevent/s rate to 406 μ A ( 343 μ A for the driver and 62.5 μA for the receiver) for an event rate below 10 Kevent/s, therefore achieving a rate dependent power saving of up to 40 times, while keeping switching times at 1.5 ns. Maximum achievable event rate was 13.7 Meps at 638 Mbps serial bit rate. Additionally, differential voltage swing is tunable, thus allowing further power reductions.

Multitechnology (I-UWB and OFDM) Coexistent Communications on the Power Delivery Network

To improve the performance and to support novel command and control applications in the smart-grid context, novel or alternative transmission schemes can be used in combination with existent power-line communication (PLC) solutions that are based on multicarrier or narrowband single carrier modulation schemes. In this respect, it is fundamental to ensure the coexistence between different systems yet respecting electromagnetic-compatibility (EMC) constraints. We consider the deployment of impulsive-ultrawideband (I-UWB) modulation for low-data-rate PLC. First, we study the design of the modulation parameters as a function of the application scenario. We consider the in-home, the outdoor low-voltage, and the outdoor medium-voltage scenario. Furthermore, we discuss EMC aspects and, according to the norms, we derive the limits for the power spectral density of the I-UWB signal. Then, we study the coexistence between existing orthogonal frequency-division multiplexing (OFDM) PLC solutions and I-UWB when they (partly) share the spectrum. We focus on the physical layer and we perform the analysis in terms of maximum achievable rate. The results show that I-UWB is suitable for low-data-rate applications and, further, it can coexist with existing OFDM PLC systems.

Joint Optimization of the Transmit Covariance and Relay Precoder in General Gaussian Amplify-and-Forward Relay Channels

The maximum data rate that can be achieved by the strictly causal full-duplex amplify-and-forward (AF) scheme in general Gaussian relay channels is achieved by Gaussian codebooks and can be cast as the solution of an optimization problem of the input transmit covariance and relay precoder. This problem possesses an intricate nonconvex structure and is hence difficult to solve. To circumvent this difficulty, the relay precoder is assumed to be given and then the Karush-Kuhn-Tucker conditions are used to obtain closed form expressions for the optimal input covariance corresponding to that precoder. These expressions are used to show that subdiagonal precoders suffice to attain the maximum achievable rate of the AF scheme at any source transmit power. In addition to significantly reducing the effort expended in searching for the optimal relay precoder, this observation enables us to find the optimal precoders at low and high source transmit powers. For asymptotically low transmit powers, the optimal relaying mechanism is shown to possess an interlacing structure, thereby resembling half-duplex operation. In contrast, for asymptotically high transmit powers, it is optimal for the relay to be silent. The asymptotic analysis enables us to develop an explicit formulation for a suboptimal precoder that, at intermediate source transmit powers, are shown numerically to outperform asymptotically optimal precoders.

Physical Layer Network Coding Based on Integer Forcing Precoded Compute and Forward

In this paper, we address the implementation of physical layer network coding (PNC) based on compute and forward (CF) in relay networks. It is known that the maximum achievable rates in CF-based transmission is limited due to the channel approximations at the relay. In this work, we propose the integer forcing precoder (IFP), which bypasses this maximum rate achievability limitation. Our precoder requires channel state information (CSI) at the transmitter, but only that of the channel between the transmitter and the relay, which is a feasible assumption. The overall contributions of this paper are three-fold. Firstly, we propose an implementation of CF using IFP and prove that this implementation achieves higher rates as compared to traditional relaying schemes. Further, the probability of error from the proposed scheme is shown to have up to 2 dB of gain over the existent lattice network coding-based implementation of CF. Secondly, we analyze the two phases of transmission in the CF scheme, thereby characterizing the end-to-end behavior of the CF and not only one-phase behavior, as in previous proposals. Finally, we develop decoders for both the relay and the destination. We use a generalization of Bezout’s theorem to justify the construction of these decoders. Further, we make an analytical derivation of the end-to-end probability of error for cubic lattices using the proposed scheme.

On Cooperative and Malicious Behaviors in Multirelay Fading Channels

Multirelay networks exploit spatial diversity by transmitting user's messages through multiple relay paths. Most works in the literature on cooperative or relay networks assume that all terminals are fully cooperative and neglect the effect of possibly existing malicious relay behaviors. In this work, we consider a multirelay network that consists of both cooperative and malicious relays, and aims to obtain an improved understanding on the optimal behaviors of these two groups of relays via information-theoretic mutual information games. By modeling the set of cooperative relays and the set of malicious relays as two players in a zero-sum game with the maximum achievable rate as the utility, the optimal transmission strategies of both types of relays are derived by identifying the Nash equilibrium of the proposed game. Our main contributions are twofold. First, a generalization to previous works is obtained by allowing malicious relays to either listen or attack in Phase 1 (source-relay transmission phase). This is in contrast to previous works that only allow the malicious relays to listen in Phase 1 and to attack in Phase 2 (relay-destination transmission phase). The latter is shown to be suboptimal in our problem. Second, the impact of CSI knowledge at the destination on the optimal attack strategy that can be adopted by the malicious relays is identified. In particular, for the more practical scenario where the interrelay CSI is unknown at the destination, the constant attack is shown to be optimal as opposed to the commonly considered Gaussian attack.

Achievable rate region for the multiple-access channel with multiple cognitive transmitters

A scenario where one ‘dumb’ radio and multiple cognitive radios communicating simultaneously with a common receiver is considered. In this paper, we derive an achievable rate region of the multiple-user cognitive multiple-access channel (MUCMAC) under both additive white Gaussian noise (AWGN) channel and rayleigh fading channel, by using a combination of multiple user dirty paper coding (DPC) and superposition coding. Through cognition, it is assumed that the secondary users (SUs) are able to obtain the message of the primary user (PU) non-causally beforehand. Using this side information, the SUs can perform multiple user DPC to avoid the interference from the SU. Besides, the SUs can also allocate part of their transmit power to aid the PU, using superposition coding. Therefore, the capacity region of traditional multiple-access channel (MAC) can be enlarged. Moreover, some asymptotic results are shown as the number of SUs increases. In the AWGN case, it is illustrated that the maximum achievable rate of the PU grows logarithmically with the increase of the number of SUs, whereas in the Rayleigh case, we show that the cognitive gain will increase with the decreasing of the channel signal to noise ratio (SNR).

Dual Analysis of the Capacity of Spectrum Sharing Cognitive Radio with MRC under Nakagami-m Fading

In this study, the maximum achievable information transmission rate of spectrum sharing cognitive radio with maximal ratio combining (MRC) antenna diversity technique is investigated when the channel between the secondary transmitter and the primary receiver and that between the secondary transmitter and the secondary receiver suffer Nakagami-m fading. With an assumption that both channels encounter Nakagami-m fading and the transmission of the secondary transmitter is subject to average interference power constraint, the approximated expressions for analyzing the effective capacity and the ergodic capacity of cognitive radio users with MRC are presented. The two capacity models are compared. In the case of the effective capacity, it is shown that different applications or users with different quality of service (QoS) requirements can be supported in cognitive radio, and when the delay QoS decreases, the effective capacity approaches the ergodic capacity.

Conflict-Aware Relay Selection for Multicast in MUD based Wireless Networks

Multipoint Relays (MPR) [1] selection is a good step toward building a very proficient routing scheme for multicast/broadcast communications. It considers the fact that data transmitted by a node is overheard by all the users in the sender’s communication range, called the Wireless Broadcast Advantage (WBA) [2][4][6]. However, when a node elects its MPR nodes it does not consider their channel qualities (i.e. they do not consider the Multi-User Diversity (MUD) [3][5] factor), that has a significant influence on the network performance. Many other works consider the MUD and the rate adaptation (RA) features [15][16]. However these works are distorted by severe simplifications that are made about some common wireless network problems such as: the number of transmissions, the access scheduling, the interference conflicts, etc. In this paper, we introduce three new MUD, WBA and RA based relay selection schemes. The first one proposed, called the Efficient Multi-user Diversity based Relay (E-MDR) selection scheme, is done over steps by exploiting the channel qualities in term of maximum achievable data rate (or channel capacity). The proposed EMDR based flooding strategy achieves the best multicast throughput without considering concurrent transmissions. It aims jointly (i) to reduce the number of relays, (ii) to maximize the throughput of each single multicast session (or partition), (iii) to reduce the number of transmissions, (iv) to exploit extremely the offered link capacities and as a consequence (v) to enhance the allover network throughput. The second MUD, WBA and RA based relay selection scheme, called the Conflict free Multi-user Diversity based Relay (C-MDR) selection scheme, performs relay selection with consideration of the interference factor. It targets (i) to select relay nodes and their data transmission rates that maximize the multicast throughput, (ii) to consider the effect of access scheduling when choosing relay nodes and (iii) to resolve conflict problems. Finally, the EC-MDR is proposed to do a compromise between C-MDR and E-MDR.

Joint power and rate allocation for spectrum sharing cognitive radio multicast networks under service outage constraint

This letter considers a downlink spectrum sharing cognitive radio (CR) multicast network coexisting with a primary network. The problem of joint power and rate allocation to maximize the average sum rate is studied. In this regard, a joint power and rate allocation scheme is proposed, where the allocated rate can be higher than the lowest rate of all the secondary users (SUs) within the same group, which is different from the conventional multicast transmission scheme. To guarantee the quality of service (QoS) of the SU, the service outage probability defined as the probability that the maximum achievable rate of the SU is lower than the rate of the group, is constrained to be under a certain threshold, which is termed as the service outage constraint. The numerical results show that the proposed scheme provides significant improvement over the conventional scheme in terms of average sum rate.

CLACK: Cross-layer ACK-Aided Opportunistic Transmission in Wireless Networks

Wi-Fi has gained tremendous attention from the research community, yielding successful technological advancements. However, the data throughput efficiency (the ratio of application throughput to the maximum achievable physical data rate) degrades rapidly as the PHY data rate increases when using the current 802.11 medium access control (MAC) protocol. To address this MAC inefficiency, many protocols have been introduced and standardized. This paper describes and examines these state-of-the-art enhancements to MAC efficiency for the 802.11 standard, and proposes a CLACK (Cross-Layer ACK) method that tackles this issue in totally different manner to those previous schemes. The main idea is simple: When a receiver sends an ACK, it transmits the data using the ACK transmission opportunity, and avoids channel contention necessary for data transmissions. The receiver's short signature is piggybacked in the PHY instead of the MAC to acknowledge the packet reception. We have implemented CLACK using USRP toolkits and GNU Software Define Radio. Our implementation demonstrates the feasibility of our key techniques for both PHY and MAC design. Further, we use detailed simulation to evaluate CLACK in general wireless environments under different traffic loads and varying channel conditions. Our results show that CLACK gains up to 52 % in terms of throughput, when compared to the basic 802.11 scheme, and up to 18 % when compared to existing advanced 802.11e/n schemes.

A Study on the Optimal Receiver Impedance for SNR Maximization in Broadband PLC

We consider the design of the front-end receiver for broadband power line communications. We focus on the design of the input impedance that maximizes the signal-to-noise ratio (SNR) at the receiver. We show that the amplitude, rather than the power, of the received signal is important for communication purposes. Furthermore, we show that the receiver impedance impacts the amplitude of the noise term. We focus on the background noise, and we propose a novel description of the noise experienced at the receiver port of a PLC network. We model the noise as the sum of four uncorrelated contributions, that is, the active, resistive, receiver, and coupled noise components. We study the optimal impedance design problem for real in-home grids that we assessed with experimental measurements. We describe the results of the measurement campaign, and we report the statistics of the optimal impedance. Hence, we study the best attainable performance when the optimal receiver impedance is deployed. We focus on the SNR and the maximum achievable rate, and we show that power matching is suboptimal with respect to the proposed impedance design approach.