A survey of single and multi-hop link schedulers for mmWave wireless systems
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paper_title: Augmenting data center networks with multi-gigabit wireless links

paper_content:

The 60 GHz wireless technology that is now emerging has the potential to provide dense and extremely fast connectivity at low cost. In this paper, we explore its use to relieve hotspots in oversubscribed data center (DC) networks. By experimenting with prototype equipment, we show that the DC environment is well suited to a deployment of 60GHz links contrary to concerns about interference and link reliability. Using directional antennas, many wireless links can run concurrently at multi-Gbps rates on top-of-rack (ToR) switches. The wired DC network can be used to sidestep several common wireless problems. By analyzing production traces of DC traffic for four real applications, we show that adding a small amount of network capacity in the form of wireless flyways to the wired DC network can improve performance. However, to be of significant value, we find that one hop indirect routing is needed. Informed by our 60GHz experiments and DC traffic analysis, we present a design that uses DC traffic levels to select and adds flyways to the wired DC network. Trace-driven evaluations show that network-limited DC applications with predictable traffic workloads running on a 1:2 oversubscribed network can be sped up by 45% in 95% of the cases, with just one wireless device per ToR switch. With two devices, in 40% of the cases, the performance is identical to that of a non-oversubscribed network.
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paper_title: Robust Topology Engineering in Multiradio Multichannel Wireless Networks

paper_content:

Topology engineering concerns with the problem of automatic determination of physical layer parameters to form a network with desired properties. In this paper, we investigate the joint power control, channel assignment, and radio interface selection for robust provisioning of link bandwidth in infrastructure multiradio multichannel wireless networks in presence of channel variability and external interference. To characterize the logical relationship between spatial contention constraints and transmit power, we formulate the joint power control and radio-channel assignment as a generalized disjunctive programming problem. The generalized Benders decomposition technique is applied for decomposing the radio-channel assignment (combinatorial constraints) and network resource allocation (continuous constraints) so that the problem can be solved efficiently. The proposed algorithm is guaranteed to converge to the optimal solution within a finite number of iterations. We have evaluated our scheme using traces collected from two wireless testbeds and simulation studies in Qualnet. Experiments show that the proposed algorithm is superior to existing schemes in providing larger interference margin, and reducing outage and packet loss probabilities.
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paper_title: 60 GHz Wireless: Up Close and Personal

paper_content:

To meet the needs of next-generation high-data-rate applications, 60 GHz wireless networks must deliver Gb/s data rates and reliability at a low cost. In this article, we surveyed several ongoing challenges, including the design of cost-efficient and low-loss on-chip and in-package antennas and antenna arrays, the characterization of CMOS processes at millimeter-wave frequencies, the discovery of efficient modulation techniques that are suitable for the unique hardware impairments and frequency selective channel characteristics at millimeter-wave frequencies, and the creation of MAC protocols that more effectively coordinate 60 GHz networks with directional antennas. Solving these problems not only provides for wireless video streaming and interconnect replacement, but also moves printed and magnetic media such as books and hard drives to a lower cost, higher reliability semiconductor form factor with wireless connectivity between and within devices.
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paper_title: On-Body Propagation at 60 GHz

paper_content:

The on-body propagation at 60 GHz is studied analytically, numerically and experimentally using a skin-equivalent phantom. First, to provide analytical-based fundamental models of path gain, the theory of propagating waves near a flat phantom is studied by considering vertical and horizontal elementary dipoles. The analytical models are in excellent agreement with full-wave simulations. For a vertically polarized wave, a minimum power decay exponent of 3.5 is found. Then, propagation on the body is investigated experimentally in vertical and horizontal polarizations using two linearly-polarized open-ended waveguides. The analytical models fit very well with the measurements. Furthermore, the effect of polarization on the antenna performance is studied numerically and experimentally.
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paper_title: On 60 GHz wireless link performance in indoor environments

paper_content:

The multi-Gbps throughput potential of 60 GHz wireless interfaces make them an attractive technology for next-generation gigabit WLANs. For increased coverage, and improved resilience to human-body blockage, beamsteering with high-gain directional antennas is emerging to be an integral part of 60 GHz radios. However, the real-world performance of these state-of-the-art radios in typical indoor environments has not previously been explored well in open literature. ::: ::: To this end, in this paper, we address the following open questions: how do these radios perform in indoor line-of-sight(LOS) and non-line-of-sight (NLOS) locations? how sensitive is performance to factors such as node orientation or placement? how robust is performance to human-body blockage and mobility? Our measurement results from a real office setting, using a first-of-its-kind experimental platform (called Presto), show that, contrary to conventional perception, state-of-the-art 60 GHz radios perform well even in NLOS locations, in the presence of human-body blockage and LOS mobility. While their performance is affected by node (or more precisely, antenna array) orientation, simply using a few more antenna arrays and dynamically selecting amongst them shows potential to address this issue. The implications of these observations is in lowering the barriers to their adoption in next-generation gigabit WLANs.
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paper_title: Robust Topology Engineering in Multiradio Multichannel Wireless Networks

paper_content:

Topology engineering concerns with the problem of automatic determination of physical layer parameters to form a network with desired properties. In this paper, we investigate the joint power control, channel assignment, and radio interface selection for robust provisioning of link bandwidth in infrastructure multiradio multichannel wireless networks in presence of channel variability and external interference. To characterize the logical relationship between spatial contention constraints and transmit power, we formulate the joint power control and radio-channel assignment as a generalized disjunctive programming problem. The generalized Benders decomposition technique is applied for decomposing the radio-channel assignment (combinatorial constraints) and network resource allocation (continuous constraints) so that the problem can be solved efficiently. The proposed algorithm is guaranteed to converge to the optimal solution within a finite number of iterations. We have evaluated our scheme using traces collected from two wireless testbeds and simulation studies in Qualnet. Experiments show that the proposed algorithm is superior to existing schemes in providing larger interference margin, and reducing outage and packet loss probabilities.
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paper_title: Beam switching support to resolve link-blockage problem in 60 GHz WPANs

paper_content:

In this paper, we propose a solution to resolve link blockage problem in 60 GHz WPANs. Line-of-Sight (LOS) link is easily blocked by a moving person, which is concerned as one of the severe problems in 60 GHz systems. Beamforming is a feasible technique to resolve link blockage by switching the beam path from LOS link to a Non-LOS (NLOS) link. We propose and evaluate two kinds of Beam Switching (BS) mechanisms: instant decision based BS and environment learning based BS. We examine these mechanisms in a typical indoor WPAN scenario. Extensive simulations have been carried out, and our results reveal that combining angle-of-arrival with the received signal to noise ratio could make better decision for beam switching. Our work provides valuable observations for beam switching during point-to-point communication using 60 GHz radio.
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paper_title: Directional MAC Protocol for Millimeter Wave based Wireless Personal Area Networks

paper_content:

Recently, up to 7 GHz license-free spectrum around 60 GHz has been allocated worldwide for high data rate wireless communications. This enables the deployment of WPANs at 60 GHz for short-range multimedia applications up to gigabits per second. In this paper we propose a new scheme to increase the efficiency of MAC layer protocol for WPANs at 60 GHz when directional antennas are used. Our scheme is based on an adaptation of the current IEEE 15.3 standard MAC protocol for WPANs on two aspects. Firstly, we propose a rate-adaptation based scheme to coordinate the directional and omni-directional transmissions in WPANs. Secondly, we propose a novel channel time allocation algorithm, which enables spatial reuse TDMA. The analytical results reveal that our algorithm significantly increases the system capacity.
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paper_title: Enhanced MAC layer protocol for millimeter wave based WPAN

paper_content:

The IEEE 802.15.3 standard defines a widely-accepted MAC layer protocol for high data rate WPANs. However, resource allocation schemes are not specified in the IEEE 802.15.3 MAC. In this paper, an enhanced IEEE 802.15.3 MAC is proposed for 60 GHz based WPANs. The enhancement relies on a novel resource management scheme. By exploiting the advanced features of the 60 GHz technology, e.g. the usage of direction antennas, our resource management scheme could realize spatial reuse TDMA in 60 GHz based WPANs. We have implemented our protocol in OPNET. Based on this simulation platform we have evaluated the advantages of using our additions to the IEEE 802.15.3 MAC. We show that our enhanced MAC protocol significantly improves the throughput and delay characteristics in 60 GHz based WPANs.
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paper_title: Scalable Heuristic STDMA Scheduling Scheme for Practical Multi-Gbps Millimeter-Wave WPAN and WLAN Systems

paper_content:

This paper proposes a hybrid SDMA/TDMA scalable heuristic scheduling scheme for throughput enhancement in practical multi-Gbps millimeter-wave systems with directional antenna. A theoretical cross layer design framework is proposed taking into consideration the MAC layer, PHY layer and millimeter-wave propagation channels based on actual measurements. The proposed generalized framework can be well suited into two of the most prominent industrial wireless communication standards, namely IEEE 802.15.3c WPAN and IEEE 802.11ad WLAN. Employing the developed theoretical framework, evaluation for throughput and error performance is conducted with validation of computer simulations. Firstly, it is found that the proposed STDMA scheme is capable of improving system throughput in the order of typically 4 to 8dB. Secondly, the proposed scheduling scheme offers superior design flexibility through its scalability features, with the optimum heuristic order observed at the 13-th order, a reasonably low value considering the performance enhancement that can be obtained. Lastly, the typical allowable interference in a network due to coexisting communication links sharing the same time slot is recommended to be controlled below -20dB. Numerical results other then the typical findings are detailed in the paper.
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paper_title: Rex: A randomized EXclusive region based scheduling scheme for mmWave WPANs with directional antenna

paper_content:

Millimeter-wave (mmWave) transmissions are promising technologies for high data rate (multi-Gbps) Wireless Personal Area Networks (WPANs). In this paper, we first introduce the concept of exclusive region (ER) to allow concurrent transmissions to explore the spatial multiplexing gain of wireless networks. Considering the unique characteristics of mmWave communications and the use of omni-directional or directional antennae, we derive the ER conditions which ensure that concurrent transmissions can always outperform serial TDMA transmissions in a mmWave WPAN. We then propose REX, a randomized ER based scheduling scheme, to decide a set of senders that can transmit simultaneously. In addition, the expected number of flows that can be scheduled for concurrent transmissions is obtained analytically. Extensive simulations are conducted to validate the analysis and demonstrate the effectiveness and efficiency of the proposed REX scheduling scheme. The results should provide important guidelines for future deployment of mmWave based WPANs.
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paper_title: CTAP-Minimized Scheduling Algorithm for Millimeter-Wave-Based Wireless Personal Area Networks

paper_content:

Beamforming is used in IEEE 802.15.3c networks to avoid high propagation attenuation and path loss and improve the overall system throughput by exploiting spatial channel reuse. In this paper, we introduce design challenges of scheduling in beamforming-enabled IEEE 802.15.3c networks. These challenges include positioning, axis alignment, and interference relation verification. We then propose a joint design of axis alignment, positioning, and scheduling. The objectives of the proposed joint design are to reduce the consumed channel time, increase the degree of spatial channel reuse, and improve the channel utilization. For positioning, we define and prove a sufficient condition for anchor selection to improve positioning accuracy. The designed channel time allocation period (CTAP)-minimized scheduling algorithm is depicted as a two-layer flow graph, and it consists of the following three phases: 1) layer-1 edge construction; 2) layer-2 edge construction; and 3) scheduling. Through the observation of transmission and reception beams, we define a rule to verify the interference relation of two flows. In addition, given correct topology information, we prove that CTAP-minimized uses the least time to serve all data flows. We evaluate and compare our algorithm with existing approaches through simulations. The observed performance metrics include utilized channel time, system throughput, scheduling efficiency, and spatial channel reuse degree. The results show that CTAP-minimized performs well and achieves its objectives.
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paper_title: Virtual time-slot allocation scheme for throughput enhancement in a millimeter-wave multi-Gbps WPAN system

paper_content:

This paper proposes a virtual time-slot allocation (VTSA) scheme for throughput enhancement to realize a multi-Gbps time division multiple access (TDMA) wireless personal area network (WPAN) system in a realistic millimeter-wave residential multipath environment. TDMA system without time-slot-reuse mechanism conventionally allocates one TDMA time-slot to only one communication link at a time. In the proposed VTSA scheme, taking advantage on the large path loss in the millimeterwave band, a single TDMA time-slot can be reallocated and reused by multiple communication links simultaneously (hence the name virtual), thus significantly increasing system throughput. On the other hand, allowing multiple communication links to occupy the same time-slot causes the generation of co-channel interference (CCI). The cross layer VTSA scheme is therefore designed to be able to maximize the throughput improvement by adaptively scheduling the sharing of time-slots, and at the same time monitor the potential performance degradation due to CCI. As a result, it is found that the VTSA scheme is capable of improving system throughput as much as 30% in both AWGN and multipath channels (line-of-sight (LOS) and non-line-of-sight (NLOS) environment). Additionally, by coupling with higher-order modulation schemes, the system is able to achieve up to a maximum throughput of 3.8 Gbps. It is also observed that higher-order modulations although have higher maximum achievable throughput in low CCI environment, the tolerance against increasing CCI is considerably lower than that of the lower-order modulations.
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paper_title: An improved ER scheduling algorithm based spatial reuse scheme for mmWave WPANs

paper_content:

This article focuses on improving the system capacity of 60GHz wireless personal area networks (WPANs) and puts forward an effective spatial reuse scheme which combines the existing exclusive region (ER) based scheduling algorithm with simple power control. In the study, the concept of ER for concurrent transmissions is introduced first. Considering the large path loss in the millimeter-wave (mmWave) band and the characteristics of typical indoor multipath channels, we modify the signal propagation model as well as ER radius for 60GHz WPANs. Then we propose an improved ER based scheduling algorithm which adopts power control instead of constant transmitting power. In the algorithm, devices are assumed to receive data at the receiver sensitivity, which refers to the minimum receiving power to ensure the reliability for communications. Computer simulations evaluate an excellent performance of the proposed spatial reuse scheme at channel capacity. In addition, the impact of the receiver sensitivity on the system is discussed.
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paper_title: Directional CSMA/CA Protocol with Spatial Reuse for mmWave Wireless Networks

paper_content:

In recent years, the millimeter wave (mmWave) technology has gained considerable interest due to the huge unlicensed bandwidth (i.e., up to 7GHz) available in the 60GHz band in most part of world. In this paper, we investigate the problem of medium access control (MAC) in mmWave wireless networks, within which directional antennas are used to combat the high path loss incurred in the 60GHz band. We extend a directional CSMA/CA protocol presented in our prior work by exploiting spatial reuse. The proposed protocol adopts virtual carrier sensing and allows non-interfering links to communicate simultaneously. We present a performance analysis as well as simulations to evaluate the proposed protocol. Our results show that the directional MAC with spatial reuse can achieve considerable performance improvements over the 802.11 MAC and the protocol proposed in our prior work. It introduces low protocol overhead and has robust performance even when the network is heavily congested.
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paper_title: STDMA-based scheduling algorithm for concurrent transmissions in directional millimeter wave networks

paper_content:

In this paper, a concurrent transmission scheduling algorithm is proposed to enhance the resource utilization efficiency for multi-Gbps millimeter-wave (mmWave) networks. Specifically, we exploit spatial-time division multiple access (STDMA) to improve the system throughput by allowing both non-interfering and interfering links to transmit concurrently, considering the high propagation loss at mmWave band and the utilization of directional antenna. Concurrent transmission scheduling in mmWave networks is formulated as an optimization model to maximize the number of flows scheduled in the network such that the quality of service (QoS) requirement of each flow is satisfied. We further decompose the optimization problem and propose a flip-based heuristic scheduling algorithm with low computational complexity to solve the problem. Extensive simulations demonstrate that the proposed algorithm can significantly improve the network performance in terms of network throughput and the number of supported flows.
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paper_title: Scheduling with Reusability Improvement for Millimeter Wave Based Wireless Personal Area Networks

paper_content:

IEEE 802.15.3c has recently been formed for developing a millimeter-wave (mmWave)-based wireless personal area networks (WPANs). It utilizes 60 GHz license-free spectrum and provides very high data rate (over 3 Gbps). To deal with the problems of high propagation attenuation and path loss, beamforming antennas are utilized. In this paper, we consider the characteristics of beamforming to design an efficient scheduling algorithm. Specifically, we integrate axis alignment and location determination into scheduling mechanism. The designed scheduling algorithm improves the degree of spatial and directional channel reusability and the overall system performance. We evaluate our approach through simulations. The simulation results show that the designed scheduling algorithm performs well and does achieve its objectives.
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paper_title: Beam switching support to resolve link-blockage problem in 60 GHz WPANs

paper_content:

In this paper, we propose a solution to resolve link blockage problem in 60 GHz WPANs. Line-of-Sight (LOS) link is easily blocked by a moving person, which is concerned as one of the severe problems in 60 GHz systems. Beamforming is a feasible technique to resolve link blockage by switching the beam path from LOS link to a Non-LOS (NLOS) link. We propose and evaluate two kinds of Beam Switching (BS) mechanisms: instant decision based BS and environment learning based BS. We examine these mechanisms in a typical indoor WPAN scenario. Extensive simulations have been carried out, and our results reveal that combining angle-of-arrival with the received signal to noise ratio could make better decision for beam switching. Our work provides valuable observations for beam switching during point-to-point communication using 60 GHz radio.
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paper_title: On frame-based scheduling for directional mmWave WPANs

paper_content:

Millimeter wave (mmWave) communications in the 60 GHz band can provide multi-gigabit rates for emerging bandwidth-intensive applications, and has thus gained considerable interest recently. In this paper, we investigate the problem of efficient scheduling in mmWave wireless personal area networks (WPAN). We develop a frame-based scheduling directional MAC protocol, termed FDMAC, to achieve the goal of leveraging collision-free concurrent transmissions to fully exploit spatial reuse in mmWave WPANs. The high efficiency of FDMAC is achieved by amortizing the scheduling overhead over multiple concurrent, back-to-back transmissions in a row. The core of FDMAC is a graph coloring-based scheduling algorithm, termed greedy coloring (GC) algorithm, that can compute near-optimal schedules with respect to the total transmission time with low complexity. The proposed FDMAC is analyzed and evaluated under various traffic models and patterns. Its superior performance is validated with extensive simulations.
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paper_title: Multi-User Operation in mmWave Wireless Networks

paper_content:

In this paper, we investigate the problem of multi-user spatial division multiple access (MU SDMA) operation in mmWave wireless networks, within which directional antennas are used to combat the high path loss incurred in the 60GHz band. We study the feasibility of MU SDMA in mmWave networks and propose two MAC protocols to support CSMA/CA based uplink and downlink MU SDMA transmissions. The proposed protocols adopt virtual carrier sensing and allows multiple users to communicate with an access point (AP) simultaneously. Performance analysis and simulation results both show that the proposed protocols can achieve considerable performance improvements over a system that supports only single user (SU) operation.
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paper_title: Medium Access Control for 60 GHz Outdoor Mesh Networks with Highly Directional Links

paper_content:

We investigate an architecture for multi-Gigabit outdoor mesh networks operating in the unlicensed 60 GHz "millimeter (mm) wave" band. In this band, the use of narrow beams is essential for attaining the required link ranges in order to overcome the higher path loss at mm wave carrier frequencies. However, highly directional links make standard MAC methods for interference management, such as carrier sense multiple access, which rely on neighboring nodes hearing each other, become inapplicable. In this paper, we study the extent to which we can reduce, or even dispense with, interference management, by exploiting the reduction in interference due to the narrow beamwidths and the oxygen absorption characteristic of the 60 GHz band. We provide a probabilistic analysis of the interference incurred due to uncoordinated transmissions, and show that, for the parameters considered, the links in the network can be thought of as pseudo-wired. That is, interference can essentially be ignored in MAC design, and the challenge is to schedule half-duplex transmissions in the face of the "deafness" resulting from highly directional links. We provide preliminary simulation results to validate our approach.
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paper_title: Opportunistic Spatial Reuse in IEEE 802.15.3c Wireless Personal Area Networks

paper_content:

The IEEE 802.15.3c wireless personal area network (WPAN) standard is designed to support highly directional wireless communications at the 60-GHz frequency band. Highly directional communications are helpful to reduce interference; hence, great potentials are provided for aggregate network throughput improvement via spatial reuse (SR). However, in 802.15.3c WPANs, the SR is limited in use since the 802.15.3c standard does not specify an explicit procedure for the SR. We design a new and simple scheme exploiting the SR, thus improving aggregate network throughput. In the proposed scheme, the 802.15.3c devices measure and report the measured channel status. Then, a controlling device, which is called the piconet coordinator (PNC) in the 802.15.3c WPAN, schedules resources available for each device. The simulation results demonstrate that the proposed scheme contributes to significant aggregate network throughput improvement. The proposed scheme is so simple that it can be easily employed for practical 802.15.3c devices. In addition, it is guaranteed to work well without conflicting with existing 802.15.3c operations.
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paper_title: Directional MAC Protocol for Millimeter Wave based Wireless Personal Area Networks

paper_content:

Recently, up to 7 GHz license-free spectrum around 60 GHz has been allocated worldwide for high data rate wireless communications. This enables the deployment of WPANs at 60 GHz for short-range multimedia applications up to gigabits per second. In this paper we propose a new scheme to increase the efficiency of MAC layer protocol for WPANs at 60 GHz when directional antennas are used. Our scheme is based on an adaptation of the current IEEE 15.3 standard MAC protocol for WPANs on two aspects. Firstly, we propose a rate-adaptation based scheme to coordinate the directional and omni-directional transmissions in WPANs. Secondly, we propose a novel channel time allocation algorithm, which enables spatial reuse TDMA. The analytical results reveal that our algorithm significantly increases the system capacity.
---
paper_title: Enhanced MAC layer protocol for millimeter wave based WPAN

paper_content:

The IEEE 802.15.3 standard defines a widely-accepted MAC layer protocol for high data rate WPANs. However, resource allocation schemes are not specified in the IEEE 802.15.3 MAC. In this paper, an enhanced IEEE 802.15.3 MAC is proposed for 60 GHz based WPANs. The enhancement relies on a novel resource management scheme. By exploiting the advanced features of the 60 GHz technology, e.g. the usage of direction antennas, our resource management scheme could realize spatial reuse TDMA in 60 GHz based WPANs. We have implemented our protocol in OPNET. Based on this simulation platform we have evaluated the advantages of using our additions to the IEEE 802.15.3 MAC. We show that our enhanced MAC protocol significantly improves the throughput and delay characteristics in 60 GHz based WPANs.
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paper_title: Angle of arrival extended S-V model for the 60 GHz wireless indoor channel

paper_content:

In this paper we measure and characterize 55-65 GHz wireless channels for a typical indoor environment. An Angle of Arrival (AoA) Modified Saleh-Valenzuela (S-V) model is used. Key AoA Modified S-V model parameters such as cluster decay factor, ray decay factor, cluster arrival rate, ray arrival rate and aoa ray angular standard deviation are extracted from the measured data.
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paper_title: Augmenting data center networks with multi-gigabit wireless links

paper_content:

The 60 GHz wireless technology that is now emerging has the potential to provide dense and extremely fast connectivity at low cost. In this paper, we explore its use to relieve hotspots in oversubscribed data center (DC) networks. By experimenting with prototype equipment, we show that the DC environment is well suited to a deployment of 60GHz links contrary to concerns about interference and link reliability. Using directional antennas, many wireless links can run concurrently at multi-Gbps rates on top-of-rack (ToR) switches. The wired DC network can be used to sidestep several common wireless problems. By analyzing production traces of DC traffic for four real applications, we show that adding a small amount of network capacity in the form of wireless flyways to the wired DC network can improve performance. However, to be of significant value, we find that one hop indirect routing is needed. Informed by our 60GHz experiments and DC traffic analysis, we present a design that uses DC traffic levels to select and adds flyways to the wired DC network. Trace-driven evaluations show that network-limited DC applications with predictable traffic workloads running on a 1:2 oversubscribed network can be sped up by 45% in 95% of the cases, with just one wireless device per ToR switch. With two devices, in 40% of the cases, the performance is identical to that of a non-oversubscribed network.
---
paper_title: Millimeter Wave WPAN: Cross-Layer Modeling and Multi-Hop Architecture

paper_content:

The 7 GHz of unlicensed spectrum in the 60 GHz band offers the potential for multiGigabit indoor wireless personal area networking (WPAN). With recent advances in the speed of silicon (CMOS and SiGe) processes, low-cost transceiver realizations in this "millimeter (mm) wave" band are within reach. However, mm wave communication links are more fragile than those at lower frequencies (e.g., 2.4 or 5 GHz) because of larger propagation losses and reduced diffraction around obstacles. On the other hand, directional antennas that provide directivity gains and reduction in delay spread are far easier to implement at mm-scale wavelengths. In this paper, we present a cross-layer modeling methodology and a novel multihop medium access control (MAC) architecture for efficient utilization of 60 GHz spectrum, taking into account the preceding physical characteristics. We propose an in-room WPAN architecture in which every link is constrained to be directional, for improved power efficiency (due to directivity gains) and simplicity of implementation (due to reduced delay spread). We develop an elementary diffraction-based model to determine network link connectivity, and define a multihop MAC protocol that accounts for directional transmission/reception, procedures for topology discovery and recovery from link blockages.
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paper_title: 3D beamforming for wireless data centers

paper_content:

Contrary to prior assumptions, recent measurements show that data center traffic is not constrained by network bisection bandwidth, but is instead prone to congestion loss caused by short traffic bursts. Compared to the cost and complexity of modifying data center architectures, a much more attractive option is to augment wired links with flexible wireless links in the 60 GHz band. Current proposals, however, are severely constrained by two factors. First, 60 GHz wireless links are limited by line-of-sight, and can be blocked by even small obstacles between the endpoints. Second, even beamforming links leak power, and potential interference will severely limit concurrent transmissions in dense data centers. In this paper, we explore the feasibility of a new wireless primitive for data centers, 3D beamforming. We explore the design space, and show how bouncing 60 GHz wireless links off reflective ceilings can address both link blockage and link interference, thus improving link range and number of current transmissions in the data center.
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paper_title: Millimeter Wave WPAN: Cross-Layer Modeling and Multi-Hop Architecture

paper_content:

The 7 GHz of unlicensed spectrum in the 60 GHz band offers the potential for multiGigabit indoor wireless personal area networking (WPAN). With recent advances in the speed of silicon (CMOS and SiGe) processes, low-cost transceiver realizations in this "millimeter (mm) wave" band are within reach. However, mm wave communication links are more fragile than those at lower frequencies (e.g., 2.4 or 5 GHz) because of larger propagation losses and reduced diffraction around obstacles. On the other hand, directional antennas that provide directivity gains and reduction in delay spread are far easier to implement at mm-scale wavelengths. In this paper, we present a cross-layer modeling methodology and a novel multihop medium access control (MAC) architecture for efficient utilization of 60 GHz spectrum, taking into account the preceding physical characteristics. We propose an in-room WPAN architecture in which every link is constrained to be directional, for improved power efficiency (due to directivity gains) and simplicity of implementation (due to reduced delay spread). We develop an elementary diffraction-based model to determine network link connectivity, and define a multihop MAC protocol that accounts for directional transmission/reception, procedures for topology discovery and recovery from link blockages.
---
paper_title: Augmenting data center networks with multi-gigabit wireless links

paper_content:

The 60 GHz wireless technology that is now emerging has the potential to provide dense and extremely fast connectivity at low cost. In this paper, we explore its use to relieve hotspots in oversubscribed data center (DC) networks. By experimenting with prototype equipment, we show that the DC environment is well suited to a deployment of 60GHz links contrary to concerns about interference and link reliability. Using directional antennas, many wireless links can run concurrently at multi-Gbps rates on top-of-rack (ToR) switches. The wired DC network can be used to sidestep several common wireless problems. By analyzing production traces of DC traffic for four real applications, we show that adding a small amount of network capacity in the form of wireless flyways to the wired DC network can improve performance. However, to be of significant value, we find that one hop indirect routing is needed. Informed by our 60GHz experiments and DC traffic analysis, we present a design that uses DC traffic levels to select and adds flyways to the wired DC network. Trace-driven evaluations show that network-limited DC applications with predictable traffic workloads running on a 1:2 oversubscribed network can be sped up by 45% in 95% of the cases, with just one wireless device per ToR switch. With two devices, in 40% of the cases, the performance is identical to that of a non-oversubscribed network.
---
paper_title: Robust Topology Engineering in Multiradio Multichannel Wireless Networks

paper_content:

Topology engineering concerns with the problem of automatic determination of physical layer parameters to form a network with desired properties. In this paper, we investigate the joint power control, channel assignment, and radio interface selection for robust provisioning of link bandwidth in infrastructure multiradio multichannel wireless networks in presence of channel variability and external interference. To characterize the logical relationship between spatial contention constraints and transmit power, we formulate the joint power control and radio-channel assignment as a generalized disjunctive programming problem. The generalized Benders decomposition technique is applied for decomposing the radio-channel assignment (combinatorial constraints) and network resource allocation (continuous constraints) so that the problem can be solved efficiently. The proposed algorithm is guaranteed to converge to the optimal solution within a finite number of iterations. We have evaluated our scheme using traces collected from two wireless testbeds and simulation studies in Qualnet. Experiments show that the proposed algorithm is superior to existing schemes in providing larger interference margin, and reducing outage and packet loss probabilities.
---
paper_title: Codebook Beam Switching Based Relay Scheme for 60 GHz Anti-blockage Communication

paper_content:

A relay solution to link-blockage problem in 60GHz communication systems is proposed based on codebook beam switching. The directional link is easily blocked by a moving person and furniture, which is regarded as one of the severe problems in 60GHz systems. Beam switching mechanism is feasible to resolve link-blockage by switching beams from the blocked path to an optimal relay path. Typically, the selection of backup relay path is crucial. Based on beam training and environment learning, a beam pair sequence list (BPSL) for relay paths is proposed for accurate selection of relay path and rapid switching of communication link. The generation and evaluation of beam pair sequence are presented. Based on BPSL, a complete and closed-form link switching process is developed. Theoretical analysis and numerical results show that for IEEE 802.15.3c indoor channel model CM1, the proposed scheme has good performance in complexity, applicability and system throughput.
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paper_title: Joint Scalable Coding and Routing for 60 GHz Real-Time Live HD Video Streaming Applications

paper_content:

Transmission of high-definition (HD) video is a promising application for 60 GHz wireless links, since very high transmission rates (up to several Gbit/s) are possible. In particular we consider a sports stadium broadcasting system where signals from multiple cameras are transmitted to a central location. Due to the high pathloss of 60 GHz radiation over the large distances encountered in this scenario, the use of relays might be required. The current paper analyzes the joint selection of the routes (relays) and the compression rates from the various sources for maximization of the overall video quality. We consider three different scenarios: (i) each source transmits only to one relay and the relay can receive only one data stream, and (ii) each source can transmit only to a single relay, but relays can aggregate streams from different sources and forward to the destination, and (iii) the source can split its data stream into parallel streams, which can be transmitted via different relays to the destination. For each scenario, we derive the mathematical formulations of the optimization problem and re-formulate them as convex mixed-integer programming, which can guarantee optimal solutions. Extensive simulations demonstrate that high-quality transmission is possible for at least ten cameras over distances of 300 m. Furthermore, optimization of the video quality gives results that can significantly outperform algorithms that maximize data rates.
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paper_title: Millimeter Wave WPAN: Cross-Layer Modeling and Multi-Hop Architecture

paper_content:

The 7 GHz of unlicensed spectrum in the 60 GHz band offers the potential for multiGigabit indoor wireless personal area networking (WPAN). With recent advances in the speed of silicon (CMOS and SiGe) processes, low-cost transceiver realizations in this "millimeter (mm) wave" band are within reach. However, mm wave communication links are more fragile than those at lower frequencies (e.g., 2.4 or 5 GHz) because of larger propagation losses and reduced diffraction around obstacles. On the other hand, directional antennas that provide directivity gains and reduction in delay spread are far easier to implement at mm-scale wavelengths. In this paper, we present a cross-layer modeling methodology and a novel multihop medium access control (MAC) architecture for efficient utilization of 60 GHz spectrum, taking into account the preceding physical characteristics. We propose an in-room WPAN architecture in which every link is constrained to be directional, for improved power efficiency (due to directivity gains) and simplicity of implementation (due to reduced delay spread). We develop an elementary diffraction-based model to determine network link connectivity, and define a multihop MAC protocol that accounts for directional transmission/reception, procedures for topology discovery and recovery from link blockages.
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paper_title: Wireless networking with directional antennas for 60 GHz systems

paper_content:

60 GHz wireless networks have the potential to support high data rate applications, but have short range transmission limitations due to larger propagation losses and reduced diffraction around obstacles. On the other hand, directional antennas are easier to implement at millimeter wavelengths and can provide benefits such as spatial reuse and higher transmission range. This paper proposes a network architecture for 60 GHz wireless personal area networks (WPANs) using directional antennas. It describes protocols for neighbor discovery, medium access, and multi-hop route establishment that exploit directional antennas to improve network performance and maintain connectivity. As a result, the proposed method can be used as a practical, low-cost solution to overcome the difficulty of short range and large propagation loss in 60 GHz systems.
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paper_title: A robust 60 GHz wireless network with parallel relaying

paper_content:

The challenge at millimeter-wave frequencies is that the propagation characteristics approximates to that of light. In a nonline-of-sight scenario, when even the mobile station (MS) is near the base station, the attenuation may be tens of dBs due to shadowing and obstructions. Increasing the number of base stations reduces such effects but at the expense of cost and complexity. An attractive method to mitigate such shadowing effects is to use dedicated active or passive relay stations. Proposed here is a network infrastructure in the form of a 3D pyramid. It consists of a single access point with four (but not restricted to) active relays operating in parallel in a medium sized room of 400 m/sup 2/. Simulation is performed in a sophisticated 3D ray tracing tool. Human shadowing densities of 1 person/400 m/sup 2/ up to 1 person/1 m/sup 2/ are set to test the robustness of such a system. Results show that comparing to a normal system with just a single access point either mounted on the ceiling or at the same level as a MS; the pyramid relaying system provides superior coverage and capacity.
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paper_title: 3D beamforming for wireless data centers

paper_content:

Contrary to prior assumptions, recent measurements show that data center traffic is not constrained by network bisection bandwidth, but is instead prone to congestion loss caused by short traffic bursts. Compared to the cost and complexity of modifying data center architectures, a much more attractive option is to augment wired links with flexible wireless links in the 60 GHz band. Current proposals, however, are severely constrained by two factors. First, 60 GHz wireless links are limited by line-of-sight, and can be blocked by even small obstacles between the endpoints. Second, even beamforming links leak power, and potential interference will severely limit concurrent transmissions in dense data centers. In this paper, we explore the feasibility of a new wireless primitive for data centers, 3D beamforming. We explore the design space, and show how bouncing 60 GHz wireless links off reflective ceilings can address both link blockage and link interference, thus improving link range and number of current transmissions in the data center.
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paper_title: Wireless data center networking with steered-beam mmWave links

paper_content:

This paper presents a new type of wireless networking applications in data centers using steered-beam mmWave links. By taking advantage of clean LOS channels on top of server racks, robust wireless packet-switching network can be built. The transmission latency can be reduced by flexibly bridging adjacent rows of racks wirelessly without using long cables and multiple switches. Eliminating cables and switches also reduces equipment costs as well as server installation and reconfiguration costs. Security can be physically enhanced with controlled directivity and negligible wall penetration. The aggregate data transmission BW per given volume is expected to scale as the fourth power of carrier frequency. The paper also deals with the architecture of such network configurations and a preliminary demonstration system.
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paper_title: Mirror mirror on the ceiling: flexible wireless links for data centers

paper_content:

Modern data centers are massive, and support a range of distributed applications across potentially hundreds of server racks. As their utilization and bandwidth needs continue to grow, traditional methods of augmenting bandwidth have proven complex and costly in time and resources. Recent measurements show that data center traffic is often limited by congestion loss caused by short traffic bursts. Thus an attractive alternative to adding physical bandwidth is to augment wired links with wireless links in the 60 GHz band. We address two limitations with current 60 GHz wireless proposals. First, 60 GHz wireless links are limited by line-of-sight, and can be blocked by even small obstacles. Second, even beamforming links leak power, and potential interference will severely limit concurrent transmissions in dense data centers. We propose and evaluate a new wireless primitive for data centers, 3D beamforming, where 60 GHz signals bounce off data center ceilings, thus establishing indirect line-of-sight between any two racks in a data center. We build a small 3D beamforming testbed to demonstrate its ability to address both link blockage and link interference, thus improving link range and number of concurrent transmissions in the data center. In addition, we propose a simple link scheduler and use traffic simulations to show that these 3D links significantly expand wireless capacity compared to their 2D counterparts.
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paper_title: Augmenting data center networks with multi-gigabit wireless links

paper_content:

The 60 GHz wireless technology that is now emerging has the potential to provide dense and extremely fast connectivity at low cost. In this paper, we explore its use to relieve hotspots in oversubscribed data center (DC) networks. By experimenting with prototype equipment, we show that the DC environment is well suited to a deployment of 60GHz links contrary to concerns about interference and link reliability. Using directional antennas, many wireless links can run concurrently at multi-Gbps rates on top-of-rack (ToR) switches. The wired DC network can be used to sidestep several common wireless problems. By analyzing production traces of DC traffic for four real applications, we show that adding a small amount of network capacity in the form of wireless flyways to the wired DC network can improve performance. However, to be of significant value, we find that one hop indirect routing is needed. Informed by our 60GHz experiments and DC traffic analysis, we present a design that uses DC traffic levels to select and adds flyways to the wired DC network. Trace-driven evaluations show that network-limited DC applications with predictable traffic workloads running on a 1:2 oversubscribed network can be sped up by 45% in 95% of the cases, with just one wireless device per ToR switch. With two devices, in 40% of the cases, the performance is identical to that of a non-oversubscribed network.
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paper_title: Beam switching support to resolve link-blockage problem in 60 GHz WPANs

paper_content:

In this paper, we propose a solution to resolve link blockage problem in 60 GHz WPANs. Line-of-Sight (LOS) link is easily blocked by a moving person, which is concerned as one of the severe problems in 60 GHz systems. Beamforming is a feasible technique to resolve link blockage by switching the beam path from LOS link to a Non-LOS (NLOS) link. We propose and evaluate two kinds of Beam Switching (BS) mechanisms: instant decision based BS and environment learning based BS. We examine these mechanisms in a typical indoor WPAN scenario. Extensive simulations have been carried out, and our results reveal that combining angle-of-arrival with the received signal to noise ratio could make better decision for beam switching. Our work provides valuable observations for beam switching during point-to-point communication using 60 GHz radio.
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paper_title: Joint Scalable Coding and Routing for 60 GHz Real-Time Live HD Video Streaming Applications

paper_content:

Transmission of high-definition (HD) video is a promising application for 60 GHz wireless links, since very high transmission rates (up to several Gbit/s) are possible. In particular we consider a sports stadium broadcasting system where signals from multiple cameras are transmitted to a central location. Due to the high pathloss of 60 GHz radiation over the large distances encountered in this scenario, the use of relays might be required. The current paper analyzes the joint selection of the routes (relays) and the compression rates from the various sources for maximization of the overall video quality. We consider three different scenarios: (i) each source transmits only to one relay and the relay can receive only one data stream, and (ii) each source can transmit only to a single relay, but relays can aggregate streams from different sources and forward to the destination, and (iii) the source can split its data stream into parallel streams, which can be transmitted via different relays to the destination. For each scenario, we derive the mathematical formulations of the optimization problem and re-formulate them as convex mixed-integer programming, which can guarantee optimal solutions. Extensive simulations demonstrate that high-quality transmission is possible for at least ten cameras over distances of 300 m. Furthermore, optimization of the video quality gives results that can significantly outperform algorithms that maximize data rates.
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paper_title: Millimeter Wave WPAN: Cross-Layer Modeling and Multi-Hop Architecture

paper_content:

The 7 GHz of unlicensed spectrum in the 60 GHz band offers the potential for multiGigabit indoor wireless personal area networking (WPAN). With recent advances in the speed of silicon (CMOS and SiGe) processes, low-cost transceiver realizations in this "millimeter (mm) wave" band are within reach. However, mm wave communication links are more fragile than those at lower frequencies (e.g., 2.4 or 5 GHz) because of larger propagation losses and reduced diffraction around obstacles. On the other hand, directional antennas that provide directivity gains and reduction in delay spread are far easier to implement at mm-scale wavelengths. In this paper, we present a cross-layer modeling methodology and a novel multihop medium access control (MAC) architecture for efficient utilization of 60 GHz spectrum, taking into account the preceding physical characteristics. We propose an in-room WPAN architecture in which every link is constrained to be directional, for improved power efficiency (due to directivity gains) and simplicity of implementation (due to reduced delay spread). We develop an elementary diffraction-based model to determine network link connectivity, and define a multihop MAC protocol that accounts for directional transmission/reception, procedures for topology discovery and recovery from link blockages.
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paper_title: Improving 60 GHz Indoor Connectivity with Relaying

paper_content:

The 60 GHz technology has a great potential to provide wireless communication at multi-gigabit rates in future home networks. To maintain the network connectivity with 60 GHz links, which are highly susceptible to propagation and penetration losses, is a major challenge. The quality and the robustness of the 60 GHz links can be improved by employing relay nodes in the network. In this paper, the contribution of relaying to the connectivity and the quality of the 60 GHz radio links is studied by modeling three indoor scenarios. It is analytically and through simulations shown that having a relay node in a 60 GHz network decreases the average freespace path loss 33% in the worst case scenario. The effects of relay device position and the obstacle density on the improvement of the average received signal level are investigated with a verified 3D ray tracing tool. A comparative simulation study on the performance of different relay configurations under various network conditions is conducted. The results yield that even a single relay device positioned at the height of other nodes can improve 50% of the links in considerable levels in a 60 GHz indoor network. It is also shown that additional relay nodes do not contribute to 60 GHz indoor connectivity significantly, if there are two properly positioned relay devices in a network which is moderately populated.
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paper_title: Multi-Hop Concurrent Transmission in Millimeter Wave WPANs with Directional Antenna

paper_content:

Millimeter-wave (mmWave) communications is a promising enabling technology for high rate (Giga-bit) multimedia applications. However, because oxygen absorption peaks at 60 GHz, mmWave signal power degrades significantly over distance. Therefore, a traffic flow transmitting over multiple short hops is preferred to improve flow throughput. In this paper, we first design a hop selection metric for the piconet controller (PNC) to select appropriate relay hops for a traffic flow, aiming to improve the flow throughput and balance the traffic load across the network. We then propose a multi-hop concurrent transmission (MHCT) scheme to exploit the spatial capacity of the mmWave WPAN. Extensive simulations show that the proposed MHCT scheme can significantly improve the traffic flow throughput and network throughput.
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paper_title: Directional Relay with Spatial Time Slot Scheduling for mmWave WPAN Systems

paper_content:

In this paper, we propose a spacial time slot scheduling algorithm for relay operation to improve the throughput performance of millimeter-wave wireless personal area network (mmWave WPAN) systems which employ directional antenna. The upcoming mmWave WPAN is designed for high definition TV (HDTV) transmission, high speed wireless docking and gaming, etc. Based on the fact that the significant path loss of millimeter-wave environments provides good space isolation, we have proposed a coexistence mechanism by sharing time slots for relay with direct transmission to guarantee throughput for the above data-rate-greedy applications. This paper is an extension that addresses spacial time slot scheduling for relay operation taking the effect of directional antenna into consideration. We model the throughput maximization with scheduling as an integer optimization and solve it by transforming the problem to a max-weight matching problem of a bipartite graph. We propose a scheduling algorithm based on the Kuhn-Munkres algorithm which can be used to solve the max weight matching problem. Simulation results show that there is up to 25% throughput improvement achieved compared with random scheduling method.
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paper_title: Deflect Routing for Throughput Improvement in Multi-Hop Millimeter-Wave WPAN System

paper_content:

In this paper, we propose a cross-layer deflect routing scheme that improves effective throughput of multi-hop millimeter-wave wireless personal area network (mmWave WPAN) system. The upcoming mmWave WPAN is designed to provide Gbps-order transmission capability, targeting applications like high definition TV (HDTV) transmission, high speed wireless docking and gaming etc. Adopting multi-hop relay offers solutions to the issues existing in mmWave WPAN system such as limited coverage range caused by the significant path loss, dramatic communication link change due to the unexpected blockage of the line-of-sight (LOS) path etc. However, multi-hop relay on the other hand decreases the effective throughput because of the required extra time. As a result, the compromised throughput may not be able to support the above applications which are greedy for data rate. Inspired by the fact that the significant path loss of millimeter-wave environment can provide good space isolation, our proposed scheme manages to improve the multi-hop throughput by sharing time slots for relay path with direct path for other transmissions. We also propose two algorithms, namely random fit deflect routing (RFDR) and best fit deflect routing (BFDR), to find the relay path on which the interference due to time slot sharing is low enough to guarantee the concurrent transmissions. Computer simulations show that, in realistic 60GHz environment, the effective multi-hop throughput can be improved up to 45%.
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Title: A survey of single and multi-hop link schedulers for mmWave wireless systems

Section 1: INTRODUCTION
Description 1: In this section, write about the advances and significance of 60 GHz, or Millimeter-Wave (mmWave), communications, regulatory changes, and their implications for future wireless networks. Mention challenges such as high path loss, link blockage problems, and potential solutions involving directional antennas and relay nodes.

Section 2: SINGLE HOP
Description 2: Discuss the implementation of single-hop communication in 60 GHz systems, primarily focusing on the IEEE 802.15.3c specification. Review various algorithms and methods for scheduling non-interfering links to maximize spatial reuse and network capacity.

Section 3: MULTI-HOP
Description 3: Explain the link blockage problem unique to 60 GHz systems and the necessity for multi-hop communication. Describe the types of relays (active and passive) used to overcome this issue and examine specific protocols and algorithms designed to maintain network connectivity and optimize relay placement.

Section 4: Active Relays
Description 4: Detail the different strategies involving active relays for maintaining network connectivity, such as discovery processes, normal operation modes, and handling of lost nodes. Highlight specific protocols and their methodologies for employing active relays in dynamic network environments.

Section 5: Passive Relays
Description 5: Explore the use of passive relays to address link blockage, especially in fixed network scenarios like data centers. Discuss various positioning strategies and scheduling algorithms that exploit ceiling reflectors or strategically placed passive relays to enhance coverage and capacity.

Section 6: HYBRID APPROACHES
Description 6: Illustrate approaches that combine spatial reuse with relay path selection to maximize network throughput. Review algorithms such as random fit deflect routing (RFDR) and best fit deflect routing (BFDR) and consider concurrent transmission schemes that utilize multi-hop routes efficiently.

Section 7: CONCLUSION
Description 7: Summarize the key problems and solutions discussed throughout the survey. Highlight areas where future research is needed, including distributed solutions for maximizing both spatial reuse and transmission data rates, optimizing passive relay placement, and minimizing transmission delays in video applications.

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