nan Asaduzzaman

Ergodic and outage capacity of interference temperature-limited cognitive radio multi-input multi-output channel

In this study, we consider a cognitive radio multi-input multi-output (CR-MIMO) system in which the cognitive radio (CR) users are allowed to access the spectrum of the licensed primary users, provided that interference power received at the primary receiver is less than a certain threshold. The authors investigate the effect of the MIMO diversity on such multi-constraint CR-MIMO systems. They consider peak interference power constraint at the primary receiver and peak transmit power constraint at the CR transmitter. In MIMO systems, the allowable transmit power is distributed over the transmit-antennas. The power allocation problem of such CR systems is studied under both sum power and interference constraints. The authors show that the equal power allocation does not improve the ergodic capacity but improves the outage capacity over the single-input single-output (SISO) system. Transmit antenna selection (TAS) which is a special case of power allocation is also investigated. The authors show that, under the peak interference and transmit power constraint, selecting a single transmit-antenna and allocating all the power to the selected best antenna achieves the same performance as the optimal power allocation (OPA). The authors evaluate ergodic capacity and outage capacity for both power allocation- and antenna selection-based schemes. The closed-form expressions of the outage probabilities are also derived. Results show that both OPA and TAS significantly improves the capacities over the SISO system.

Cooperative relaying in interference limited cognitive radio networks

In this paper, we consider a cooperative relaying based cognitive radio (CR) networks in which the primary receivers are protected by peak interference power constraint. In such scenario, finding the transmission opportunity with a target data rate by maintaining the interference power constraint is the prime goal of the system. We show that cooperative relaying techniques can significantly reduce the outage probability equivalently, improve the transmission opportunity of the CR networks in slow-fading channels. We consider both distributed space time code (DSTC) based simultaneous transmission and single relay selection based transmission from the relays. The exact expressions of the outage probabilities of different cooperative relaying schemes are derived for arbitrary number of relays and interference power constraint in Rayleigh fading environment. Results show that the single relay selection based schemes outperform the DSTC based scheme, in terms of both outage probability and implementation complexity, in multi-relay CR network.

Optimal switching adaptive M-QAM for opportunistic amplify-and-forward networks

This paper proposes adaptive discrete modulation (ADM) for opportunistic amplify-and-forward relaying networks, designed to improve system spectral efficiency while still ensuring quality of service (QoS) constraints, i.e., the target bit error rate. Based on the limited feedback signal sent by the destination, the source adjusts the transmitted modulation constellation size according to the total instantaneous received signal-to-noise ratio (SNR) at the destination. To qualify the proposed system performance, we develop performance upper bounds for the outage probability, bit error rate and achievable spectral efficiency. From numerical results, it is confirmed that the analytic results agree closely with the empirical ones and the proposed scheme with optimal switching provides a better spectral efficiency as compared to that with fixed switching at medium SNR regime.

Coded diversity for cooperative MISO based wireless sensor networks

Motivated by the recent works on cooperative MIMO, this letter presents a coded diversity based cooperative protocol for wireless sensor networks. In densely deployed sensor networks, nearby nodes form a cluster of virtual antenna array to provide independent fading paths. The source node encodes the information bits with any channel code and forwards a portion of the codeword towards the cooperating nodes. The source and the cooperating nodes transmit different portion of the codeword to achieve a coded diversity at destination. Analysis and simulation show that our proposal can achieve full diversity when code rate is below a certain threshold.

Code Combining in Cooperative Communication

It is well known that cooperative transmission among the single antenna wireless nodes and a proper combining at destination can obtain spatial diversity. In this paper, we introduce a new form of combining technique in cooperative communication. For a coded transmission scheme code-combining can obtain a near optimal low rate code by combining repeated codewords. Instead of MRC (maximal ratio combining) based combining of received coded packets from source and relays, we propose a simple code-combining at destination. For same data, rate and power consumption code-combining offers better or similar performance with less complexity than MRC. Moreover using a puncturing technique at the relay we can get a same diversity order as MRC with reduced packet relaying time; equivalently, with higher data rate for over all system. This reduction of transmission time at relay allows us to increase the diversity order by using more than one relay for one source; where each relay forwards a punctured portion of received data. Alternatively, when the relays are not available to improve diversity order, we can use only one relay to cooperate M source nodes where all sources obtain a diversity order of 2 with a higher data rate.

On the capacity of opportunistic cooperative networks under adaptive transmission

This paper offers a study on Rayleigh channel capacity of opportunistic cooperative networks in conjunction with adaptive transmission where the source adapts its rate and/or power level according to the changing channel conditions while the best relay simply amplifies and forwards the signals. To this end, the upper and lower bound of the end-to-end effective signal-to-noise ratio (SNR) for an arbitrary number of cooperative relays equipped amplify-and-forward protocol is derived and then used to derive the closed-form expressions of the system channel capacity under three different adaptive policies: optimal simultaneous power and rate adaptation (OPRA), constant power with optimal rate adaptation (OPA) and channel inversion with fixed rate (TIFR). Our results are verified through comparison with Monte Carlo simulations where we also illustrate that, among them, for an arbitrary number of relays, TIFR gives the worst channel capacity; OPRA gives the best channel capacity and ORA has a channel capacity quality in between the others.

Coded Cooperation Diversity in Wireless Relay Network

This paper studies the application of coded cooperation in wireless relay network. In wireless relay network only one user transmit data and the cooperative users assist the active user to get the spatial diversity. Exploit the idle time of active user we get the time diversity along with the spatial diversity. We investigate the rate compatible puncture convolutional (RCPC) code based coded cooperation in a wireless relay network where two relay cooperating with one active user. The effect of various channel conditions on the cooperation is also examined.

Outage Analysis of a Cooperative Multi-hop Wireless Network for Rayleigh Fading Environment

This paper presents an information theoretic outage analysis for physical layer of a cooperative multihop wireless network. Our analysis shows that cooperation by selecting a proper relay at each hop increases the coverage or data rate of the network. In our analysis we consider both symmetric and asymmetric network model. We also investigate the availability of cooperative relay at each hop and show that end-to-end performance of the network depends on the relay selection procedure at each hop. We also verify our analytical results with simulations.

Composite Signaling Coded Cooperation for Fast and Slow Fading

Motivated by the recent works of coded cooperation this letter presents a composite signal structure based coded cooperation technique. Our proposed protocol performs well in both slow and fast fading whereas, conventional coded cooperation is ineffective in fast fading. We develop the bounds on BER and FER of our proposal. Simulations confirm our developed bound and shows that the proposed coded cooperation protocol outperforms direct transmission in both fast and slow fading environments.

Performance Analysis of Coded Cooperation based Relayed Transmission under Rayleigh Fading Channels

This paper introduces the coded cooperation protocol in wireless relay network. We propose a two relay based coded cooperation protocol with RCPC codes for wireless networks. The proposed two-relay based system can achieve a diversity of order 4 under slow fading environment. Under fast fading, the diversity order is 2 times of the free distance of the convolutional code. We develop upper bounds on BER and FER for the system under both slow and fast fading with Rayleigh distribution. The effect of various channel conditions on the cooperation is also examined in this work.