Performance analysis of multi-hop framed ALOHA systems with virtual antenna arrays

We consider a multi-hop virtual multiple-input-multiple-output system, which uses the framed ALOHA technique to select the radio resource at each hop. In this scenario, the source, destination and relaying nodes cooperate with neighboring devices to exploit spatial diversity by means of the concept of virtual antenna array. We investigate both the optimum number of slots per frame in the slotted structure and once the source-destination distance is fixed, the impact of the number of hops on the system performance. A comparison with deterministic, centralized re-use strategies is also presented. Outage probability, average throughput, and energy efficiency are the metrics used to evaluate the performance. Two approximated mathematical expressions are given for the outage probability, which represent lower bounds for the exact metric derived in the paper

Low-latency Networking: Where Latency Lurks and How to Tame It

While the current generation of mobile and fixed communication networks has been standardized for mobile broadband services, the next generation is driven by the vision of the Internet of Things and mission critical communication services requiring latency in the order of milliseconds or sub-milliseconds. However, these new stringent requirements have a large technical impact on the design of all layers of the communication protocol stack. The cross layer interactions are complex due to the multiple design principles and technologies that contribute to the layers' design and fundamental performance limitations. We will be able to develop low-latency networks only if we address the problem of these complex interactions from the new point of view of sub-milliseconds latency. In this article, we propose a holistic analysis and classification of the main design principles and enabling technologies that will make it possible to deploy low-latency wireless communication networks. We argue that these design principles and enabling technologies must be carefully orchestrated to meet the stringent requirements and to manage the inherent trade-offs between low latency and traditional performance metrics. We also review currently ongoing standardization activities in prominent standards associations, and discuss open problems for future research

Optimal transmission schemes in wireless networks and their comparison with simple ALOHA based scheme

We present our analysis and results that allow us to conjecture that maximum capacity in wireless networks can be achieved if nodes transmitting simultaneously are positioned in a hexagonal grid pattern. But obviously, it is very difficult to realize such a protocol which ensures that active transmitters in the network are positioned in any specific grid pattern. We compare the optimal capacity in networks with grid positioned transmitters with the capacity of wireless networks where nodes are dispatched according to uniform distribution and use very simple ALOHA-based protocol for channel access. We will also extend this analysis to multi-hop case and characterize the maximum throughput achievable in wireless networks with ALOHA-based protocols and TDMA and grid based TDMA protocols

Medium access control protocol design for wireless communications and networks review

Medium access control (MAC) protocol design plays a crucial role to increase the performance of wireless communications and networks. The channel access mechanism is provided by MAC layer to share the medium by multiple stations. Different types of wireless networks have different design requirements such as throughput, delay, power consumption, fairness, reliability, and network density, therefore, MAC protocol for these networks must satisfy their requirements. In this work, we proposed two multiplexing methods for modern wireless networks: Massive multiple-input-multiple-output (MIMO) and power domain non-orthogonal multiple access (PD-NOMA). The first research method namely Massive MIMO uses a massive number of antenna elements to improve both spectral efficiency and energy efficiency. On the other hand, the second research method (PD-NOMA) allows multiple non-orthogonal signals to share the same orthogonal resources by allocating different power level for each station. PD-NOMA has a better spectral efficiency over the orthogonal multiple access methods. A review of previous works regarding the MAC design for different wireless networks is classified based on different categories. The main contribution of this research work is to show the importance of the MAC design with added optimal functionalities to improve the spectral and energy efficiencies of the wireless networks

A Random Access Protocol incorporating Multi-Packet Reception, Retransmission Diversity and Successive Interference Cancellation

8th International Workshop on Multiple Access Communications (MACOM2015), Helsinki, Finland.This paper presents a random access protocol assisted by a set of signal processing tools that significantly improve the multi-packet reception (MPR) capabilities of the system. A receiver with M antennas is used to resolve collisions with multiplicity K _ M. The remaining unresolved conflicts (with multiplicity K > M) are processed by means of protocol-induced retransmissions that create an adaptive multiple-input multiple-output (MIMO) system. This scheme, also known as NDMA (network diversity multiple access) with MPR, can achieve in ideal conditions a maximum throughput of M packets/time-slot. A further improvement is proposed here, where the receiver attempts to recover the information immediately after the reception of each (re)transmission. This is different from conventional NDMA, where this decoding process only occurs once the adaptive MIMO channel is assumed to become full-rank (i.e., once the estimated number of required retransmissions has been collected). The signals that are correctly decoded at every step of the proposed algorithm are used to mitigate interference upon the remaining contending signals by means of successive interference cancellation (SIC). This allows for improved reception as well as for the reduction of the number of retransmissions required to resolve a collision. Significantly high throughput figures that surpass the nominal rate of the system (T > M) are here reported. To the best of our knowledge this is the first random access protocol that achieves this figure. Correlation between antennas and between retransmissions, as well as imperfections of SIC are also considered. In ideal conditions, the effects of SIC are equivalent to a splitting tree operation. The inclusion of SIC in NDMA-MPR also opens the possibility of backwards compatibility with legacy terminals. The protocol achieves the highest throughput in the literature of single-hop wireless random access with minimum feedback complexity. This is a significant result for future highly dense 5G networks

A Comprehensive Survey of Potential Game Approaches to Wireless Networks

Potential games form a class of non-cooperative games where unilateral improvement dynamics are guaranteed to converge in many practical cases. The potential game approach has been applied to a wide range of wireless network problems, particularly to a variety of channel assignment problems. In this paper, the properties of potential games are introduced, and games in wireless networks that have been proven to be potential games are comprehensively discussed.Comment: 44 pages, 6 figures, to appear in IEICE Transactions on Communications, vol. E98-B, no. 9, Sept. 201

Q-learning Channel Access Methods for Wireless Powered Internet of Things Networks

The Internet of Things (IoT) is becoming critical in our daily life. A key technology of interest in this thesis is Radio Frequency (RF) charging. The ability to charge devices wirelessly creates so called RF-energy harvesting IoT networks. In particular, there is a hybrid access point (HAP) that provides energy in an on-demand manner to RF-energy harvesting devices. These devices then collect data and transmit it to the HAP. In this respect, a key issue is ensuring devices have a high number of successful transmissions. There are a number of issues to consider when scheduling the transmissions of devices in the said network. First, the channel gain to/from devices varies over time. This means the efficiency to deliver energy to devices and to transmit the same amount of data is different over time. Second, during channel access, devices are not aware of the energy level of other devices nor whether they will transmit data. Third, devices have non-causal knowledge of their energy arrivals and channel gain information. Consequently, they do not know whether they should delay their transmissions in hope of better channel conditions or less contention in future time slots or doing so would result in energy overflow