Opportunistic beamforming (OB) relies on the transmission of Channel State Information (CSI) in the form of instantaneous Signal to Noise Ratio (SNR) from Mobile Stations (MSs) back to the Base Station (BS) for scheduling purposes that increase throughput and/or maintain resource allocation fairness. OB is employed in environments of low mobility and low scatter, artificially inducing channel fluctuations that can better exploit Multiuser diversity (MUD). Multiple antennas at the BS are randomly alter the channel's response and generate peaks in gain where users can be scheduled on, maximising system throughput. Additional gains are achieved by transmitting multiple weighting vectors from the BS, but their use can significantly increase the load of the feedback channel and mitigate MUD gains. Selective Multiuser diversity (SMUD) has been proposed for the original beamforming scheme as a technique that reduces feedback requirements substantially without any significant throughput degradations. This paper considers the joined use of multiple weights and SMUD in opportunistic beamforming, aiming to increase capacity while reducing feedback overhead. Results show that with an appropriate use of threshold levels, not only average throughput can be increased through the use of multiple weighting vectors but also a notable decrease in feedback load requirements compared to the conventional OB with SMUD design is achieved. The terms Mobile Station (MS) and User are used interchangeably in this paper, with the same meaning.

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. The objective of the Green Radio research programme (Core 5) of Mobile VCE is to deliver reduced power consumption of radio access networks. This paper attempts to show that an efficient exploitation of multiple antenna techniques and multiuser diversity in both the time, frequency as well as the space domain can significantly ease the power requirements of a base station, whilst maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity are examined.

Abstract-Fourth Generation Networks will almost invariably adopt OFDMA (Orthogonal Frequency Division Multiple Access) and MIMO (Multiple Input-Multiple Output technologies, in order to meet high data rate and Quality of Service (QoS) requirements. The Worldwide Interoperability for Microwave Access (WiMAX) MAC Layer, which is based on the IEEE 802.16 standard, is designed to support a variety of applications, including voice and multimedia services. The problem of providing QoS in broadband wireless systems is one of managing radio resources effectively. Efficient scheduling algorithms that balance the QoS requirements of each application and user with the available radio resources need to be developed. This paper considers a number of scheduling policies concentrating on real-time Voice over IP (VoIP) traffic. Via numerical results we show that the conventional notion of fairness fails to guarantee service for low latency applications such as VoIP for an increasing traffic load. We show better QoS is achieved via a greedy scheduling approach that manages to serve packets faster.

This paper presents a link level analysis of the rate and energy efficiency performance of the LTE downlink considering the unitary codebook based precoding scheme. In a multi-user environment, appropriate radio resource management strategies can be applied to the system to improve the performance gain by exploiting multi-user diversity in the time, frequency and space domains and the gains can be translated to energy reduction at the base station. Several existing and novel resource scheduling and allocation algorithms are considered for the LTE system in this paper. A detailed analysis of the performance gain of different algorithms in terms of throughput, rate fairness, and power efficiency is presented.

Abstract-OFDM is an attractive solution for the design of future wireless communications due to its robustness to dispersion in multipath environments. Additional diversity gains can be realised by OFDMA by exploiting not only the temporal fading, but also spectral fading, that can result in higher rates due to increased diversity. A scheduler exploiting multiuser diversity imposes strict feedback requirements as channel quality information is required for every user's feedback unit with a feedback rate at least equal to the coherence time of the channel. The instantaneous signal to noise ratio is the most commonly used metric to quantify users' channel conditions. In OFDMA, the overhead due to feedback transmission increases significantly due to the fact that signal to noise ratio is required in the frequency domain, for every subcarrier of the OFDM symbol, which can potentially mitigate any multiuser diversity gains. This paper proposes a reduced feedback OFDMA design that requires very limited feedback information on a clustered subcarrier basis, whilst maintaining high downlink rates via Opportunistic Beamforming with multiple weighting vector transmission from the Base Station. This scheme is shown to be quite robust, as it can be easily adapted to variable channel conditions without any significant increase in complexity.