Ali Eksim

Performance Improvement of Binary Sensor-Based Statistical Space-Time Block Code Cooperative Diversity Using Limited Feedback

Abstract The statistical cooperative diversity, based on space-time block codes (statistical STBC cooperative diversity) is proposed for binary sensors by several authors. Since Alamouti’s code is the only orthogonal code which achieves full diversity and full rate for two sensors, it is used in their works, and their achievable diversity order is 2. Instead of using Alamouti’s code, we use extended cooperative space-time block coding (ECBSTBC) which achieves full diversity which is shown analytically and full rate for an arbitrary number of sensors if a limited feedback is available at the active sensors. Another method to increase diversity in cooperative communications is sensor (relay) selection. However, the sensor selection method may lead to the selection of the same (near) sensor for transmission over a long period causing the energy hole problem in sensor networks. The ECBSTBC which utilizes every sensor in sight thus distributes the energy consumption among active sensors and alleviates the energy hole problem. In addition, it can be shown with detailed simulations that the ECBSTBC outperforms both the statistical STBC cooperative diversity and the sensor selection schemes.

Effective cooperative spectrum sensing in IEEE 802.22 standard with time diversity

IEEE is developing a wireless communication standard that will take place in cognitive radio class and be valid in the world. Data communication capability supporting is aimed with this standard called IEEE 802.22 to the rural area users in TV bands. In the TV bands, not to cause harmful interference to the existing TV receivers and to communicate in unused channels, effective detection of unused channels is needed. This is succeeded with effective spectrum sensing. Sensing the presence of TV signals in the channel being tracked is more possible with using effective spectrum sensing techniques. In this paper, it is demonstrated with detailed simulations that a base station and users in an IEEE 802.22 cell sense TV signals better with setting up cooperation and it is reached to the better performance results by adding time diversity to this cooperation. Besides, it is also presented in this paper that effective cooperation is done with decrease of cost, power consumption and complexity by choosing relays who have higher SNR threshold.

Diversity Enhancement with Cooperative Balanced Space-Time Block Coding

In this paper, a balanced space-time block coding method for cooperative relay networks is proposed which guarantees full diversity for any number of mobile relays with minimal delay, provided that few bits of feedback from the destination to the source and the relays are available. As in the case of orthogonal space-time block codes, all transmitted symbols are separately decoded both in the relays and the destination. Therefore, decoding complexity is linear. Many of the proposed solutions in the literature are distributed space-time codes which are designed for limited number of relays. In the proposed scheme, as many number of relays as necessary can be included to increase diversity. Moreover, the proposed scheme has better signal-to-noise ratio improvement compared to relay selection schemes. Lastly, the new method satisfies power consumption fairness among relay terminals and requires no knowledge of topology information.

Extended balanced space–time block coding with transmit antenna selection

The original proposal of the extended balanced space–time block coding (EBSTBC) and its special subsets like balanced space–time block coding utilize all available transmit antennas to guarantee full diversity and to maximize the coding gain when few bits of feedback from the destination to the source are available. Because of the construction technique of EBSTBC, an antenna out of N transmit antennas does not contribute coding gain. To prevent this, a novel EBSTBC design and transmit scheme is proposed. This scheme transmits only N − 1 antennas out of N antennas and an antenna that maximizes the received signal-to-noise ratio at the destination doubles its transmit power. The proposed scheme improves performance of the EBSTBC and its subsets and outperforms closed-loop extended orthogonal space–time block codes, phase feedback based extended space–time block codes, partial phase combining and transmit antenna selection schemes. The difference in performance becomes more prevalent in the presence of feedback errors. The proposed technique can be applied for orthogonal space–time block codes and quasi-orthogonal space–time block codes if the destination informs the source which antenna has the highest gain. Copyright

Extended Cooperative Balanced Space-Time Block Coding for Increased Efficiency in Wireless Sensor Networks

Diversity techniques for communications among sensors are very effective tool to increase reception quality and battery lifetimes. A well-known method to increase diversity in cooperative communications is sensor (relay) selection. However, sensor selection method may lead to the selection of the same (near) sensor for transmission over a long period. One of the alternative techniques to sensor selection is cooperative balanced space-time block coding which utilizes every sensor in sight, thus, distributes the energy consumption among many sensors. Furthermore, it guarantees full diversity for any number of relay sensors. In this work, we consider dual-hop amplify-and-forward wireless sensor network and extend the cooperative balanced space-time block code family to improve its performance. In the proposed scheme, a larger number of codes can be generated for improved coding gain, and better signal-to-noise ratio improvement can be obtained compared to sensor selection schemes.

Full rate full diversity cooperative Extended Balanced Space-Time Block Coding for wireless multicasting

Multicasting is a spectrally efficient method for supporting multimedia communication by allowing transmission of packets to multiple destinations using fewer resources. To incorporate cooperative (distributed MIMO) diversity, Cooperative Extended Balanced Space-Time Block Codes (CEBSTBCs) have been proposed providing full diversity when one or more feedback bits are sent back via feedback channel. However, the CEBSTBCs are designed for unicast delivery in the literature. This paper presents a novel wireless multicasting scheme which selects the optimum CEBSTBC for all mobile users to support wireless multimedia multicasting. Extensive, detailed simulations are performed to show the feasibility of full rate and full diversity multicast service provisioning in Rayleigh fading channels.

Received SNR based code and antenna selection for limited feedback communication

Code selection and transmit antenna selection are widely used in limited feedback wireless systems. When one of the antenna channel gains is much higher than the other antenna channel gains; using antenna selection method increases received SNR at the receiver. However, when antenna channel gains are close to each other; using code selection method increases the received SNR at the receiver. In this paper, we propose an adaptive code and antenna selection scheme to increase the received SNR at the destination. In this technique, using one additional bit feedback yields improved SNR at the destination compared to using solely code or transmit antenna selection method. Detailed simulations show that adaptive code and antenna selection with four bit feedback yields a performance of the extended balanced space-time block coding with ideal feedback which requires exact channel state information at the transmitter.

Transmit antenna selection for extended balanced space-time block codes

Original proposal of extended balanced space-time block coding (EBSTBC) and its special subsets like balanced space-time block coding (BSTBC) utilize all available transmit antennas to guarantee full diversity and to maximize the coding gain when few bits of feedback from the destination to the source are available. Due to construction technique of the EBSTBC, an antenna out of N transmit antennas does not contribute the coding gain. To prevent this, a novel the EBSTBC design and transmit scheme is proposed. This scheme transmits only N-1 antennas out of N antennas and an antenna which maximize the received SNR at the destination doubles its transmit power. The proposed scheme improves performance of the EBSTBC and its subsets and outperforms closed-loop extended orthogonal space-time block codes (CL-EO-STBC), phase feedback based extended space-time block codes (PFB-ESTBC), partial phase combining (PPC) and transmit antenna selection (TAS) schemes. Another advantage of the proposed scheme is allowing minimum decoding delay for the EBSTBC. The proposed technique can be applied for orthogonal space-time block codes (OSTBCs) and quasi-orthogonal space-time block codes (QOSTBCs) if the destination informs the source which antenna has the highest gain.

Improvement on Cooperative Balanced Space-Time Block Coding with relay selection

In this paper, we improve the performance of cooperative balanced space-time block codes (CBSTBC) by means of a novel relay selection method. The proposed method prevents an error floor with minimal sacrifice from the full diversity for any number of mobile relays. In the new method, the relays transmit their source-relay channel partial information to the destination with one bit and the destination informs the source and the relays about the selected balanced code and the selected relays with few bits of feedback. For a comparison, we consider distributed space time block codes (DSTBC). As expected, DSTBC perform poorly when source-relay channels have low SNR, thus, an error floor is reached. Detailed computer simulations show that, in our proposed method the occurring of the error floor shifts considerably to higher SNR region.

Cooperative spectrum sensing for mobile users

Cognitive radio is a radio communication technique, where unlicensed or cognitive users monitor the spectrum for the existence of licensed (primary) users and have a communication capability when the primary users donpsilat transmit their data. This technique needs an effective spectrum sensing because of the not disturbing the primary users. The increasing of this effectiveness is related with the higher detection probability of the existing primary users. In this paper, new cooperative spectrum sensing technique recommended for mobile users when the environment is free space line of sight (LOS). It is confirmed with this technique that the probability of detection of the primary userpsilas existence increases with the using of cooperative diversity by mobile users. It is resulted that this increasing of the detection probability is well-proportioned with relay numbers who helps target secondary user. In addition to this, systempsilas performance increases with the threshold distance of the true sensing. But it is demonstrated with the detailed simulations that the probability of detection of the primary userpsilas existence decreases with the speed of the mobile users.