Efficient Resource Management for mmWave WPANs

Millimeter Wave (mmWave) communication is considered as an enabling technology for the next generation of cellular networks because it offers much larger bandwidth and higher data rate than the current lower-frequency cellular systems to satisfy the exponential growth of mobile data demand. High gain directional antennas are needed to overcome high propagation losses in mmWave bands. However, the reliance on highly directional antennas will result in a more complicated initial cell search procedure since both base station and mobile device have to look for each other over a large space to establish the link. This paper focuses on analyzing the performance of the directional cell search procedure where the base stations periodically transmit signals in a set of optimal directional patterns to scan the coverage area. The mobile terminals detect the signals from the base station using the Generalized Likelihood Ratio Test (GLRT). The results show that with an appropriate scanning scheme, the use of directional antennas can outperform their omnidirectional counterparts in terms of signal detection performance as well as total time required.

The use of directional antennas in mobile wireless networks has emerged recently due to their numerous advantages such as high gain, low interference and low transmission power to reach the same distance as omni antennas. However, directional antennas limit the coverage and connectivity in the network. In this paper, we propose an algorithm to calculate a topology preserving map for wireless sensor networks using directional antennas. In the literature, topology mapping have been proposed for sensor networks equipped with omni antennas; however, to the best of our knowledge none of the existing work has considered the use of directional antennas in sensor network topology mapping. The application of existing algorithms in directional sensor networks will consume significantly high energy, as it requires transmitting the number of sectors times more beacon messages to cover the omini antenna range. Thus in this paper, a novel beacon forwarding algorithm limiting the number of forwarding sectors based on packet received direction is proposed. The simulation results show that it is possible to generate an accurate topology preserving map can be generated by only forwarding beacons in total of 135° angle. Moreover, the energy and the number of edges used to generate the topology map can be reduced by nearly 50% compared to the topology map generation with omni antennas based on received signal strength and hop count.

We consider ad hoc wireless networks that use directional antennas and have limited energy resources. To explore quantitatively the advantage offered by the use of directional antennas over the case of omnidirectional antennas, we consider the case of connection-oriented multicast traffic. Building upon our prior work on multicasting algorithms, we introduce two protocols that exploit the use of directional antennas and evaluate their performance, We observe significant improvement with respect to the omnidirectional case, in terms of both energy efficiency and network lifetime. Additionally, we show that further substantial increase in the network's lifetime can be achieved by incorporating a simple measure of a node's residual energy into the node's cost function.

We consider ad hoc wireless networks that use directional antennas and have limited energy resources. The performance objectives of such networks depend largely on the application. However, a robust performance measure is the total traffic volume that the network can deliver when all nodes are equipped with a finite and non-renewable amount of energy. We show that the network's lifetime can be extended significantly by incorporating a simple measure of a node's residual energy into the node's cost function. To explore quantitatively the advantage offered by the use of directional antennas over the case of omnidirectional antennas, we consider the case of connection-oriented multicast traffic. Building upon our prior work on multicasting algorithms, we introduce two protocols that exploit the use of directional antennas and evaluate their performance. We observe significant improvement with respect to the omnidirectional case.

In general, MIMO systems are associated with high scattering isotropic propagation while the use of directive antennas is associated with free space or narrow angular spread conditions. We found outdoor-indoor channels to be in between these two extremes, in the sense that we observed directivity - and - MIMO gain, for the same ensemble of channels. Our observation is based on measurements with directive (8 dB gain) and dipole antennas. Median MIMO capacities were found to be 80% of the ideal (Rayleigh i.i.d.), at 5 dB signal to noise ratio (SNR), with no significant difference resulting from the choice of antenna. On the other hand, using properly aimed directive antennas, the SNR was found on average to be 5.4 dB above that obtainable with dipoles, somewhat less than the 7 dB antenna gain difference. Thus, isotropic propagation, which would have negated directivity gains, cannot be justified in general. The combination of MIMO processing and angular search with directive antennas resulted on average in gains of 69% over the median capacities obtained with dipoles. Since MIMO and directivity can combine effectively, it may in some cases be convenient to arrange subgroups of antennas for beamforming, and then process the thus reduced number of radio channels for MIMO gain.

ADAPT: An Adaptive Directional Antenna Protocol for medium access control in Terahertz communication networks

Effective antenna selection and deployment strategies are important for reducing co-channel interference in indoor wireless systems. Low-cost solutions are essential, and strategies that utilise simple (passive) antennas (such as directional patches) are advantageous from this perspective. However, performance is always an issue and the improvements achievable through clever antenna deployment (both placement and orientation) need to be quantified. An experimental investigation of indoor propagation comparing the performance of directional and omni-directional antennas is reported. In the case study of a voice-based indoor communication system employing DS-CDMA radio access technique with BPSK modulation, the outage probability for base stations fitted with directional antennas was observed to change in the −54% to +66% range relative to the omni-directional case. The effective change in the distribution of carrier-to-interference ratios by the use of directional antennas is well established in outdoor micro cellular deployment scenarios; however, the magnitude of the influence is quantified for an indoor environment in this case study. It is also shown that obstacles in the environment can amplify the effectiveness of the antenna deployment by acting as physical cell boundaries that restrict interference. External interference has been shown to cause a significant degradation to the performance of an indoor system when the carrier-to-external-interference ratio. This performance degradation can be minimised by appropriate deployment of directional antennas at the base stations, although the optimum antenna orientations depends on the strength of external interference.

Directional antennas have numerous advantages over traditional omnidirectional antennas, which include more spatial reuse, extended range, less interference, and less energy consumption. Directional antennas introduce deafness and new hidden terminal problems. Deafness may cause more collisions, and hidden terminal problems may result in more retransmissions, poor quality of service, more energy consumption, and less packet delivery ratio. Hence, it is important to design of an effective medium access protocol specifically for directional antennas in order to reap the benefits of directional antennas while managing deafness and hidden terminal problems, otherwise the challenges can adversely affect system performance. In wireless sensor networks, the sensors are battery powered with limited supply of energy. Therefore, energy efficient protocols and solutions are immensely important with the desired goal of extending the network lifetime longer than what is possible through the omnidirectional antennas. In this thesis, I have proposed an energy efficient scheduled directional medium access control protocol (DTRAMA) which is specially designed for the wireless sensor nodes which use directional antennas in wireless sensor networks. It is a traffic adaptive scheduled medium access protocol in which nodes create their transmission and sleep schedules on the basis of their traffic. Scheduled medium access for packet transmission is used to address the deafness and hidden terminal problems caused by the use of directional communication in contention based MAC protocols. Use of directional antenna reduces interference which indirectly improves packet delivery ratio by improving the signal to noise ratio and by reducing the packet error rate. DTRAMA is energy efficient: firstly because the nodes use directional data communication which requires lower node transmit power than the omnidirectional data communication for the same transmission range; and secondly, because the nodes schedule their sleep period to reduce idle listening and overhearing which improves energy efficiency. In DTRAMA, sleep schedule of the node is traffic adaptive which is essential to maximize the sleep period. The node, by using spatial reuse checks, reuses the wireless medium to the maximum extent to reap the spatial reuse benefits of the directional antenna. The nodes reduce their packet latency through spatial reuse. Through simulation and by using different topologies, I have compared the performance of DTRAMA with those of omnidirectional schedule MAC protocol (TRAMA) and contention based directional MAC protocol (DMAC), which clearly shows that DTRAMA outperforms TRAMA and DMAC in packet delivery ratio and outperforms TRAMA in terms of packet latency.

Directional antennas have numerous advantages over traditional omnidirectional antennas, which include more spatial reuse, extended range, less interference, and less energy consumption. Directional antennas introduce deafness and new hidden terminal problems. Deafness may cause more collisions, and hidden terminal problems may result in more retransmissions, poor quality of service, more energy consumption, and less packet delivery ratio. Hence, it is important to design of an effective medium access protocol specifically for directional antennas in order to reap the benefits of directional antennas while managing deafness and hidden terminal problems, otherwise the challenges can adversely affect system performance. In wireless sensor networks, the sensors are battery powered with limited supply of energy. Therefore, energy efficient protocols and solutions are immensely important with the desired goal of extending the network lifetime longer than what is possible through the omnidirectional antennas. In this thesis, I have proposed an energy efficient scheduled directional medium access control protocol (DTRAMA) which is specially designed for the wireless sensor nodes which use directional antennas in wireless sensor networks. It is a traffic adaptive scheduled medium access protocol in which nodes create their transmission and sleep schedules on the basis of their traffic. Scheduled medium access for packet transmission is used to address the deafness and hidden terminal problems caused by the use of directional communication in contention based MAC protocols. Use of directional antenna reduces interference which indirectly improves packet delivery ratio by improving the signal to noise ratio and by reducing the packet error rate. DTRAMA is energy efficient: firstly because the nodes use directional data communication which requires lower node transmit power than the omnidirectional data communication for the same transmission range; and secondly, because the nodes schedule their sleep period to reduce idle listening and overhearing which improves energy efficiency. In DTRAMA, sleep schedule of the node is traffic adaptive which is essential to maximize the sleep period. The node, by using spatial reuse checks, reuses the wireless medium to the maximum extent to reap the spatial reuse benefits of the directional antenna. The nodes reduce their packet latency through spatial reuse. Through simulation and by using different topologies, I have compared the performance of DTRAMA with those of omnidirectional schedule MAC protocol (TRAMA) and contention based directional MAC protocol (DMAC), which clearly shows that DTRAMA outperforms TRAMA and DMAC in packet delivery ratio and outperforms TRAMA in terms of packet latency.

Several power control schemes provide lower power consumption and increase network throughput. Some of these protocol use maximum energy and some adjustable energy to transmit data. Some schemes use directional antenna transmission technique without using any power control scheme. Therefore, in this paper, we proposed a power control scheme that uses directional antenna and takes interference into account. This Power control scheme uses different power levels to transmit RTS–CTS, DATA–ACK using directional antenna. The use of directional antenna increases spatial reuse in the network. Experiment result shows that proposed scheme enhances the throughput of the network and decreases energy consumption. This power control scheme has been compared with existing IEEE 802.11, DMAC, and DBASIC schemes. Our scheme outperforms the above existing schemes in terms of throughput and energy consumption. The throughput of this scheme improves from 9 to 19% for denser to sparse networks. However, as the network density increases the performance of the proposed scheme decreases marginally, but still remains better.

The use of directional antennas in wireless ad hoc networks can significantly improve global performance due to a high spatial channel reuse. Nevertheless, its introduction poses new location dependent problems related to the MAC protocol. In this paper, the Balanced Incomplete Block Design theory has been exploited to develop a new MAC protocol for wireless ad hoc networks using directional antennas. The protocol is highly scalable. Moreover, preliminary simulation results show that it can provide a high number of concurrent communications, depending on the number of directional antennas mounted on each node, and great fairness in bandwidth sharing.

Directional antennas have been shown to have the potential to provide dramatic increases in throughput and reduction in delay, while simultaneously requiring lower transmit power and increasing LPI/LPD and A/J qualities. Among military systems, sensor systems have a strong need for such characteristics due to their inability to move, length of deployment time, as well as a need for stealth operation. In this paper we describe and analyze significant issues for contention-based MACs for directional antennas which are of particular interest to sensor systems. We also provide a MAC design that overcomes these difficulties.

The use of directional antennas and beamforming in emerging fifth-generation systems forces the development of appropriate propagation models and computational methods that give the opportunity to be considered parameters and characteristics of such antennas/beams. This paper focuses on a simulation evaluation of a radio link capacity in which the directional antennas are used. For this purpose, a multi-elliptical propagation model is used. The analysis is carried out for two different beamwidths and a variable orientation of antennas working at 28 GHz.

Throughput scaling laws of an ad hoc network equipping directional antennas at each node are analyzed. More specifically, this paper considers a general framework in which the beam width of each node can scale at an arbitrary rate relative to the number of nodes. We introduce an elastic routing protocol, which enables to increase per-hop distance elastically according to the beam width, while maintaining an average signal-to-interference-and-noise ratio at each receiver as a constant. We then identify fundamental operating regimes characterized according to the beam width scaling and analyze throughput scaling laws for each of the regimes. The elastic routing is shown to achieve a much better throughput scaling law than that of the conventional nearest-neighbor multihop for all operating regimes. The gain comes from the fact that more source-destination pairs can be simultaneously activated as the beam width becomes narrower, which eventually leads to a linear throughput scaling law. In addition, our framework is applied to a hybrid network consisting of both wireless ad hoc nodes and infrastructure nodes. As a result, in the hybrid network, we analyze a further improved throughput scaling law and identify the operating regime where the use of directional antennas is beneficial. In addition, we perform numerical evaluation in both ad hoc and hybrid networks, which completely validates our analytical results.

An exact expression for the outage probability of opportunistic relaying in a dual-hop amplify-and-forward relay network is derived for general fading environments and the case where the source and destination nodes make use of directional antennas. The relaying nodes are assumed to be distributed according to a homogeneous two-dimensional Poisson point process with fixed density. This assumption is of great practical importance as in a typical practical scenario, the number of relays as well as their distances from the source and destination are random. It is observed that under some circumstances, a directional antenna at the source may permit more efficient deployment of the relay network than the case where an omnidirectional antenna is used.