Joint Relay Selection and Power Control that aims to Maximize Sum-Rate in Multi-Hop Networks

Focusing on the joint relay selection and power control problem with a view to maximizing the sum-rate, we propose a novel sub-optimal algorithm that iterates between relay selection and power control. The relay selection is performed by maximizing the minimum signal-to-interference-plus-noise-ratio (as opposed to maximizing the sum-rate) and the power control is performed using a successive convex approximation. By comparing the proposed algorithm with existing solutions via extensive simulations, we show that the proposed algorithm results in significant sum-rate gains. Finally, we analyze the two-user multi-hop network and show that optimum transmit power of at least for two transmitting nodes can be found using binary power allocation.Comment: Extended Version, Submitted to IEEE Communications Letter

Performance Analysis of Relay Selection Schemes in Multi-Hop Decode-and-Forward Networks

This paper analyses the data rate achieved by various relay selection schemes in a single-user multi-hop relay network with decode-and-forward (DF) relaying. While the single-user relay selection problem is well studied in the literature, research on achievable rate maximization is limited to dual-hop networks and multi-hop networks with a single relay per hop. We fill this important gap by focusing on achievable rate maximization in multi-hop, multi-relay networks. First, we consider optimal relay selection and obtain two approximations to the achievable rate. Next, we consider three existing sub-optimal relay selection strategies namely hop-by-hop, ad-hoc and block-by-block relay selection and obtain exact expressions for the achievable rate under each of these strategies. We also extend the sliding window based relay selection to the DF relay network and derive an approximation to the achievable rate. Further, we investigate the impact of window size in sliding window based relay selection and show that a window size of three is sufficient to achieve most of the possible performance gains. Finally, we extend this analysis to a noise limited multi-user network where the number of available relay nodes is large compared to the number of users and derive approximations to the achievable sum-rate

Integrated Sensing and Communications for IoT: Synergies with Key 6G Technology Enablers

The Internet of Things (IoT) and wireless generations have been evolving simultaneously for the past few decades. Built upon wireless communication and sensing technologies, IoT networks are usually evaluated based on metrics that measure the device ability to sense information and effectively share it with the network, which makes Integrated Sensing and Communication (ISAC) a pivotal candidate for the sixth-generation (6G) IoT standards. This paper reveals several innovative aspects of ISAC from an IoT perspective in 6G, empowering various modern IoT use cases and key technology enablers. Moreover, we address the challenges and future potential of ISAC-enabled IoT, including synergies with Reconfigurable Intelligent Surfaces (RIS), Artificial Intelligence (AI), and key updates of ISAC-IoT in 6G standardization. Furthermore, several evolutionary concepts are introduced to open future research in 6G ISAC-IoT, including the interplay with Non-Terrestrial Networks (NTN) and Orthogonal Time-Frequency Space (OTFS) modulation.Comment: 7 pages, 6 figure

Towards Integrated Sensing and Communications for 6G: A Standardization Perspective

The radio communication division of the International Telecommunication Union (ITU-R) has recently adopted Integrated Sensing and Communication (ISAC) among the key usage scenarios for IMT-2030/6G. ISAC is envisioned to play a vital role in the upcoming wireless generation standards. In this work, we bring together several paramount and innovative aspects of ISAC technology from a global 6G standardization perspective, including both industrial and academic progress. Specifically, this article provides 6G requirements and ISAC-enabled vision, including various aspects of 6G standardization, benefits of ISAC co-existence, and integration challenges. Moreover, we present key enabling technologies, including intelligent metasurface-aided ISAC, as well as Orthogonal Time Frequency Space (OTFS) waveform design and interference management for ISAC. Finally, future aspects are discussed to open various research opportunities and challenges on the ISAC technology towards 6G wireless communications.Comment: 7 pages, 5 figure

Performance analysis of base station cooperation

© 2015 Dr. Rajitha SenanayakeBase station cooperation is envisioned to be a major component in future wireless network because of its potential to exploit interference and improve network performance. In this thesis we present a comprehensive and rigorous analytical investigation of cooperative cellular networks where multiple base stations process multiple user signals via a central processor. From a theoretical perspective, the challenge is to analytically evaluate the performance gains of cooperative networks when compared to traditional non-cooperative networks. The practical challenge is to design a realistic cooperative framework that strikes a balance between performance and complexity. First, we concentrate on a fully cooperative framework where the central processor has access to all the user signals. We adopt a general network scenario with arbitrary number of users transmitting to an arbitrary number of base stations and carry out optimal multiuser detection. Considering maximum likelihood (ML) estimation, we investigate the optimum error probability based on the pair wise error probability (PEP) bounds. We derive new bounds on the bit error probability (BEP) of an arbitrary network user when the channels are subjected to independent but not necessarily identically distributed Rayleigh fading with exponentially decaying path loss. We further extend our investigation to asymptotically characterize the BEP bounds at high signal-to-noise ratios (SNRs). For the fully cooperative framework, we observe that base station cooperation can significantly improve the error performance compared to a traditional non-cooperative network. In reality, however, collecting all the user signals at one central processor is not always feasible. As such, for large-scale distributed networks, we practically constrain the cooperation to a set of geographically neighboring base stations referred to as a cluster. Taking into account the effect of interference from out-of-cluster users, we contest the significant error probability gains obtained by fully cooperative networks and highlight that the error performance enters a saturation regime at high SNRs. To obtain further insights we extend our investigation to a mixed Rician-Rayleigh fading model where users experience a line-of-sight signal path to their nearest base station. Our new error probability results prove that base station cooperation cannot convert an interference limited network into a noise limited network. Next, we focus on the achievable rate of cluster-based cooperative networks. Based on linear minimum mean square error (LMMSE) estimation, we investigate two processing architectures, namely a centralized processing architecture and a decentralized processing architecture. In the centralized case, all the in-cluster user signals are processed at one central processor whereas in the decentralized case each base station locally estimates the in-cluster user signals before sending them to the central combiner. As such, the centralized architecture adds more overhead to the network compared to the decentralized architecture. Interestingly, our numerical examples show that the decentralized processing architecture can offer a comparable achievable rate performance to the centralized processing architecture. Finally, we consider the effect of equipping large numbers of antennas at each base station in a so-called distributed massive multiple-input multiple-output (MIMO) network. For this network, we consider a simple zero-forcing (ZF) receiver at the central processor to exploit the performance advantages of massive MIMO. To gain analytical insights, we derive a simple and an accurate approximation for the SNR of an arbitrary network user. Based on our SNR approximation, we evaluate the error probability and the achievable rate of distributed massive MIMO. Our theoretical results serve to underscore the practical implementation benefits of distributed massive MIMO in future generation cooperative cellular networks

Optimal Routing for Multi-user Multi-hop Relay Networks via Dynamic Programming

In this paper, we study the relay selection problem in multi-user, multi-hop relay networks with the objective of minimizing the maximum outage probability across all users. When only one user is present, it is well known that the optimal relay selection problem can be solved efficiently via dynamic programming. This solution breaks down in the multi-user scenario due to dependence between users. We resolve this challenge using a novel relay aggregation approach. On the expanded trellis, dynamic programming can be used to solve the optimal relay selection problem with computational complexity linear in the number of hops. Numerical examples illustrate the efficient use of this algorithm for relay networks.Comment: Extended Version, Accepted to IEEE Wireless Communications Letter

Is the policy of allowing a female labor companion feasible in developing countries? Results from a cross sectional study among Sri Lankan practitioners

Abstract Background Companionship during labor is known to have both physical and psychosocial benefits to mother and baby. Sri Lanka made a policy decision to allow a labour companion in 2011. However, implementation has been unsatisfactory. Given the leading role Obstetricians play in the implementation of policy, a study was undertaken to assess the knowledge, attitudes and practices among them. Method A descriptive cross sectional study was conducted among consultant obstetricians working in the state hospitals using the platform ‘Survey Monkey’. Results Out of the 140 consultant obstetricians invited, 68(48.5%) participated. Among the study participants, 40 (58.8%) did not allow labour companions in their wards. Lack of space (n = 32; 80%) and the volume of work in the labor wards (n = 22; 55%) were the commonest reasons for not allowing a companion. Only 16.7% (n = 5) of the obstetricians handling more than 300 deliveries per month allowed a companion (p = 0.001). Less than 50% of the obstetricians were aware of the advantages associated with the practice such as shorter labor, lesser analgesic requirement, higher chances of a normal birth, improved neonatal outcome and reduced requirements for labor augmentation for slow progress of labor. Knowledge on advantages on breast feeding and reduced need of instrumental delivery also remained low. Conclusion In an individual unit, the consultant often decides policy. The study points out the need to improve awareness among the practitioners

Analytical handle for ZF reception in distributed massive MIMO

Comunicació presentada a la 50th Asilomar Conference on Signals, Systems and Computers, celebrada els dies 6 a 9 de novembre de 2016 a Pacific Grove, Califòrnia.This paper considers distributed massive MIMO networks where a large number of antennas, either collocated or geographically scattered over a region, communicate with mobile users. This communication is impaired by interference from similar transmissions in adjacent regions and by noise. Focusing on zero-forcing (ZF) reception, we derive simple expressions that very accurately approximate the instantaneous signal-to-interference-plus-noise ratio (SINR) and the ergodic spectral efficiency of an arbitrary user. These expressions enable short-cutting any assessment of the network-level performance, either analytical or simulation-based.Work supported by Project TEC2015-66228-P (MINECO/FEDER, UE)

Analytical handle for ZF reception in distributed massive MIMO

Comunicació presentada a la 50th Asilomar Conference on Signals, Systems and Computers, celebrada els dies 6 a 9 de novembre de 2016 a Pacific Grove, Califòrnia.This paper considers distributed massive MIMO networks where a large number of antennas, either collocated or geographically scattered over a region, communicate with mobile users. This communication is impaired by interference from similar transmissions in adjacent regions and by noise. Focusing on zero-forcing (ZF) reception, we derive simple expressions that very accurately approximate the instantaneous signal-to-interference-plus-noise ratio (SINR) and the ergodic spectral efficiency of an arbitrary user. These expressions enable short-cutting any assessment of the network-level performance, either analytical or simulation-based.Work supported by Project TEC2015-66228-P (MINECO/FEDER, UE)