Wireless communication has become a key technology for competitiveness of next generation vehicles. Recently, the 3GPP has initiated standardization activities for LTE-based V2X services composed of vehicle-to-vehicle, vehicle-to-pedestrian, and vehicle-to-infrastructure/ network. The goal of these 3GPP activities is to enhance LTE systems to enable vehicles to communicate with other vehicles, pedestrians, and infrastructure in order to exchange messages for aiding in road safety, controlling traffic flow, and providing various traffic notifications. In this article, we provide an overview of the service flow and requirements of the V2X services LTE systems are targeting. This article also discusses the scenarios suitable for operating LTE-based V2X services, and addresses the main challenges of high mobility and densely populated vehicle environments in designing technical solutions to fulfill the requirements of V2X services. Leveraging the spectral-efficient air interface, the cost-effective network deployment, and the versatile nature of supporting different communication types, LTE systems along with proper enhancements can be the key enabler of V2X services.Hanbyul Seo and Ki-Dong Lee are with LG Electronics; Shinpei Yasukawa is with NTT DoCoMo; Ying Peng is with CATT; Philippe Sartori is with Huawei.
Interference alignment is a signaling technique that provides high
multiplexing gain in the interference channel. It can be extended to multi-hop
interference channels, where relays aid transmission between sources and
destinations. In addition to coverage extension and capacity enhancement,
relays increase the multiplexing gain in the interference channel. In this
paper, three cooperative algorithms are proposed for a multiple-antenna
amplify-and-forward (AF) relay interference channel. The algorithms design the
transmitters and relays so that interference at the receivers can be aligned
and canceled. The first algorithm minimizes the sum power of enhanced noise
from the relays and interference at the receivers. The second and third
algorithms rely on a connection between mean square error and mutual
information to solve the end-to-end sum-rate maximization problem with either
equality or inequality power constraints via matrix-weighted sum mean square
error minimization. The resulting iterative algorithms converge to stationary
points of the corresponding optimization problems. Simulations show that the
proposed algorithms achieve higher end-to-end sum-rates and multiplexing gains
that existing strategies for AF relays, decode-and-forward relays, and direct
transmission. The first algorithm outperforms the other algorithms at high
signal-to-noise ratio (SNR) but performs worse than them at low SNR. Thanks to
power control, the third algorithm outperforms the second algorithm at the cost
of overhead.Comment: submitted to IEEE Transactions on Signal Processing in December 2011,
revised in April 2012 and in September 201
This paper considers techniques to increase the performance of a broadband wireless OFDM system through adaptation in both the time and frequency domains. System throughput estimates are provided for frequency non-selective coding (coding for frequency diversity across subcarriers) and frequency selective coding (e.g., DSL) for single antenna, Alamouti, and selective closed-loop MIMO configurations. Additional gains from performing multi-user frequency-domain scheduling are achieved and determined using proportional fair and maximum (subcarrier) C/I schedulers. The performance gains of multi-dimensional adaptation and scheduling techniques are contrasted with the amount of feedback required. Measured data from a 20 MHz experimental system and turbo coding simulations are used to estimate the size of each feedback report, and an accepted user speed distribution is used to estimate an appropriate feedback rate.
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