mmWave (millimeter-Wave) is a very promising technology for the future wireless communication. To mitigate its high attenuation characteristics, mmWave communication frequently employs directional beamforming for both transmission and reception. Localization commonly takes advantage of directionality in RF frequencies in urban and indoor environments. In this paper, we use lessons learned from classical RF-based localization for discussing a set of feasible localization approaches in the context of mmWave bands. We further map the requirements of each discussed localization approach to design requirements for future mmWave devices and assess the expected accuracy of such approaches for a set of realistic scenarios. Our results show that mmWave-based localization is promising in both its availability and accuracy, even in the presence of a limited number of localization anchor nodes.

This paper evaluates and compares the performance of single- user (SU) and multi-user (MU) transmission for downlink multiple-input multiple-output (MIMO) channels in terms of system energy efficiency (EE). We introduce power control algorithms to maximize EE. Specifically, to optimize the power allocation, we consider the problem of EE maximization with the satisfaction of the minimum spectral efficiency (SE) gain. Antenna selection is taken into account to further enhance the EE performance for both SU and MU systems. Our results reveal that we should turn off extra antennas at the transmitter, which are originally used for diversity gain but incur large circuit power consumption. Our comparisons between SU and MU differ from conventional comparisons, which focus on SE. Jointly considering EE and SE, we show that SU is more desirable when the transmit power is low, while MU is favored in the case of high transmit power.

A user scheduling problem for downlink multiuser-multiple-input-multiple-output (MU-MIMO) systems is investigated. Unlike in theoretical analysis, users are usually equipped with different numbers of antennas in practical downlink systems, which we call receive antenna heterogeneity. We propose a scheduling algorithm which utilizes the property of receiver antenna heterogeneity to improve the system's throughput. The algorithm consists of two strategies: (1) divide the whole set of users into several groups where each group contains multiple users served simultaneously; (2) allocate spatial streams to users in each group such that sum rate is maximized. Simulation results are provided to show that our algorithm outperforms the homogeneous scheduling algorithm which does not take the heterogeneity into account.

Multipacket reception (MPR) refers to physical layers where receivers can decode multiple simultaneously transmitted packets. In this paper we investigate the resulting performance of conjoining carrier sense multiple access (CSMA) communications with MPR. We report on its maximum achievable stable throughput with decentralized control and show there can be throughput gain over slotted ALOHA (S-ALOHA), the non-channel-sensing protocol of choice. However, this gain diminishes as the physical layer's MPR strength increases, thereby diminishing the need for channel sensing. Nonetheless, for systems evolving from a single-user (SU) to a multiple-user (MU) channel, CSMA can furnish significantly more efficient utilization of MPR capacity than S-ALOHA. This is meaningful in practice because the emerging generation of the widely deployed IEEE 802.11 wireless local area networks (WLAN) - 802.11ac - is adapting MPR and will operate in said region. In that regard, we also discuss the effective usage of a channel's resources for MPR and highlight the advantages multiuser-MIMO (MU-MIMO), an MPR technique, can offer to WLANs. Using early design specifications of 802.11ac, we show that the existing SU-oriented 802.11 MAC parameters can under-utilize the MPR capacity offered by a MU-oriented physical layer.

While there has been much research on the capacity of the collision channel for multiple access protocols, there has been little investigation on their fundamental performance with multipacket reception (MPR)-capable channels, which allow more than one simultaneous transmissions to be successfully received. In this paper we investigate the properties of these MPR channels and provide an upper bound for their multiaccess capacities with a genie-aided argument. Our results not only give insights into the limiting efficiency with which multiaccessing can be performed in the MPR environment, but also generalize familiar results from classical multiaccess theory.

An orthogonal frequency division multiplexing system suffers performance degradation when the length of the cyclic prefix is less than the channel impulse response. The root cause of this degradation is the inter-carrier interference (ICI) and inter-symbol interference (ISI) introduced by the excessive multipath delay. Generally, multiple-input multiple-output (MIMO) beamforming is helpful in mitigating such interference because it can spatially suppress some of the multipath. However, the effectiveness of this suppression is very limited. In this paper, we propose an ICI/ISI-aware beamforming algorithm which explicitly takes into account the multipath characteristic of the channel. Optimal steering vectors are derived to maximize the signal-to-interference-plus-noise ratio. This technique not only achieves the beamforming benefit, but also significantly mitigates the ICI and ISI. We show, via simulations, that the proposed algorithm can dramatically reduce the block error rate, permitting good performance for channel delay profiles that would break conventional links. This is vitally important for the extension of indoor wireless LAN designs to outdoor uses.

Due to constraints inherent in RF systems, it is commonly agreed that collision detection is not feasible for CSMA-based wireless networks. However, by applying ideas from the busy-tone solution for hidden terminals and engineering together existing solutions for RF communications, we devise a simple method to reliably detect collisions for the wireless channel. We investigate the throughput gain delivered by CSMA/CD and its cross-layer designed version for multipacket-reception capable physical layers. We show that collision detection can help the system operate closer to its channel capacity. Our novel performance-improving protocols can be applied as beneficial extensions to the IEEE 802.11 wireless LAN standards

The finite battery power in wireless portable computing devices is a motivating factor for developing energy efficient wireless network technologies. This paper investigates energy efficiency, relating it to throughput and packet delay for both non-persistent and p-persistent CSMA, two protocols popularly applied in current wireless networks; for example, the widely adopted IEEE 802.11 WLAN standards are based on p-persistent CSMA. For high message generation by the members of a finite population, we find that non-persistent CSMA has a markedly higher energy efficiency than p-persistent CSMA for all network configurations, though the latter attains a moderately lower packet delay. We also show that when non-persistent CSMA is optimized for energy efficiency, throughput and delay are impacted negatively, whereas p-persistent CSMA can effectively optimize all three with the same network settings. Our results help illuminate the suitability of each CSMA scheme for various wireless environments and applications.