Multi-Round Contention in Wireless LANs with Multipacket Reception

Multi-packet reception (MPR) has been recognized as a powerful capacity-enhancement technique for random-access wireless local area networks (WLANs). As is common with all random access protocols, the wireless channel is often under-utilized in MPR WLANs. In this paper, we propose a novel multi-round contention random-access protocol to address this problem. This work complements the existing random-access methods that are based on single-round contention. In the proposed scheme, stations are given multiple chances to contend for the channel until there are a sufficient number of ``winning" stations that can share the MPR channel for data packet transmission. The key issue here is the identification of the optimal time to stop the contention process and start data transmission. The solution corresponds to finding a desired tradeoff between channel utilization and contention overhead. In this paper, we conduct a rigorous analysis to characterize the optimal strategy using the theory of optimal stopping. An interesting result is that the optimal stopping strategy is a simple threshold-based rule, which stops the contention process as soon as the total number of winning stations exceeds a certain threshold. Compared with the conventional single-round contention protocol, the multi-round contention scheme significantly enhances channel utilization when the MPR capability of the channel is small to medium. Meanwhile, the scheme automatically falls back to single-round contention when the MPR capability is very large, in which case the throughput penalty due to random access is already small even with single-round contention

Enabling Millimeter Wave Communication for 5G Cellular Networks: MAC-layer Perspective

Data traffic among mobile devices increases dramatically with emerging high-speed multimedia applications such as uncompressed video streaming. Many new applications beyond personal communications involve tens or even hundreds of billions wireless devices, such as wireless watch, e-health sensors, and wireless glass. The number of wireless devices and the data rates will continue to grow exponentially. Quantitative evidences forecast that total data rate by 2020 will be 1000 times of current 4G data rate. Next generation wireless networks need fundamental changes to satisfy the overwhelming capacity demands. Millimeter wave (mmWave) communication with huge available bandwidth is a very promising solution for next generation wireless networks to overcome the global bandwidth shortage at saturated microwave spectrum. The large available bandwidth can be directly translated into high capacity. mmWave communication has several propagation characteristics including strong pathloss, atmospheric and rain absorption, low diffraction around obstacles and penetration through objects. These propagation characteristics create challenges for next generation wireless networks to support various kinds of emerging applications with different QoS requirements. Our research focuses on how to effectively and efficiently exploit the large available mmWave bandwidth to achieve high capacity demand while overcoming these challenges on QoS provisioning for various kinds of applications. This thesis focuses on MAC protocol design and analysis for mmWave communication to provide required capacity and QoS to support various kinds of applications in next generation wireless networks. Specifically, from the transmitter/receiver perspective, multi-user beamforming based on codebook is conducted to determine best transmission/reception beams to increase network capacity considering the mutual interferences among concurrent links. From the channel perspective, both interfering and non-interfering concurrent links are scheduled to operate simultaneously to exploit spatial reuse and improve network capacity. Link outage problem resulting from the limited diffraction capability and low penetration capability of mmWave band is addressed for quality provisioning by enabling multi-hop transmission to replace the link in outage (for low-mobility scenarios) and buffer design with dynamic bandwidth allocation among all the users in the whole coverage area (for high-mobility scenarios). From the system perspective, system structure, network architecture, and candidate MAC are investigated and novel backoff mechanism for CSMA/CA is proposed to give more transmission opportunity to faraway nodes than nearby nodes in order to achieve better fairness and higher network capacity. In this thesis, we formulate each problem mentioned above as an optimization problem with the proposed algorithms to solve it. Extensive analytical and simulation results are provided to demonstrate the performance of the proposed algorithms in several aspects, such as network capacity, energy efficiency, link connectivity and so on

Performance analysis and protocol design for multipacket reception in wireless networks.

Zheng, Pengxuan.Thesis (M.Phil.)--Chinese University of Hong Kong, 2007.Includes bibliographical references (leaves 53-57).Abstracts in English and Chinese.Abstract --- p.iAcknowledgments --- p.vTable of Contents --- p.viList of Figures --- p.viiiList of Tables --- p.ixChapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Motivation --- p.1Chapter 1.2 --- Related Work --- p.2Chapter 1.3 --- Our Contribution --- p.3Chapter 1.4 --- Organization of the Thesis --- p.4Chapter Chapter 2 --- Background Overview --- p.6Chapter 2.1.1 --- Traditional Wireless Networks --- p.6Chapter 2.2 --- Exponential Backoff --- p.7Chapter 2.2.1 --- Introduction --- p.7Chapter 2.2.2 --- Algorithm --- p.8Chapter 2.2.3 --- Assumptions --- p.9Chapter 2.3 --- System Description --- p.9Chapter 2.3.1 --- MPR Capability --- p.9Chapter 2.3.2 --- Backoff Slot --- p.10Chapter 2.3.3 --- Carrier-sensing and Non-carrier-sensing Systems --- p.11Chapter Chapter 3 --- Multipacket Reception in WLAN --- p.12Chapter 3.1 --- MAC Protocol Description --- p.13Chapter 3.2 --- Physical Layer Methodology --- p.16Chapter 3.2.1 --- Blind RTS Separation --- p.17Chapter 3.2.2 --- Data Packet Detection --- p.19Chapter Chapter 4 --- Exponential Backoff with MPR --- p.21Chapter 4.1 --- Analytical Model --- p.22Chapter 4.1.1 --- Markov Model --- p.22Chapter 4.1.2 --- Relations betweenpt andpc --- p.23Chapter 4.2 --- Simulation Settings --- p.26Chapter 4.3 --- Asymptotic Behavior of Exponential Backoff --- p.27Chapter 4.3.1 --- Convergence ofpt andpc --- p.27Chapter 4.3.2 --- Convergence of Npt --- p.29Chapter Chapter 5 --- Non-carrier-sensing System --- p.31Chapter 5.1 --- Performance Analysis --- p.31Chapter 5.1.1 --- Throughput Derivation --- p.31Chapter 5.1.2 --- Throughput Analysis --- p.32Chapter 5.1.3 --- Convergence of S --- p.36Chapter 5.2 --- Infinite Population Model --- p.38Chapter 5.2.1 --- Attempt Rate --- p.38Chapter 5.2.2 --- Asymptotic Throughput of Non-carrier-sensing System --- p.39Chapter Chapter 6 --- Carrier-sensing System --- p.43Chapter 6.1 --- Throughput Derivation --- p.43Chapter 6.2 --- Asymptotic Behavior --- p.44Chapter Chapter 7 --- General MPR Model --- p.48Chapter Chapter 8 --- Conclusions --- p.51Bibliography --- p.5

Stability Region of a Slotted Aloha Network with K-Exponential Backoff

Stability region of random access wireless networks is known for only simple network scenarios. The main problem in this respect is due to interaction among queues. When transmission probabilities during successive transmissions change, e.g., when exponential backoff mechanism is exploited, the interactions in the network are stimulated. In this paper, we derive the stability region of a buffered slotted Aloha network with K-exponential backoff mechanism, approximately, when a finite number of nodes exist. To this end, we propose a new approach in modeling the interaction among wireless nodes. In this approach, we model the network with inter-related quasi-birth-death (QBD) processes such that at each QBD corresponding to each node, a finite number of phases consider the status of the other nodes. Then, by exploiting the available theorems on stability of QBDs, we find the stability region. We show that exponential backoff mechanism is able to increase the area of the stability region of a simple slotted Aloha network with two nodes, more than 40\%. We also show that a slotted Aloha network with exponential backoff may perform very near to ideal scheduling. The accuracy of our modeling approach is verified by simulation in different conditions.Comment: 30 pages, 6 figure