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A reduced signaling scheme based on a new metric for opportunistic beamforming

IP.com Disclosure Number: IPCOM000030024D
Original Publication Date: 2004-Aug-25
Included in the Prior Art Database: 2004-Aug-25
Document File: 2 page(s) / 83K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

A fundamental characteristic of the wireless channel is the fading of the channel strength due to constructive and destructive interference between multipaths. An important means to cope with channel fading is the use of diversity. Multiuser diversity is a form of diversity inherent in a wireless network, provided by independent time-varying channels across the different users. The diversity benefit is exploited by tracking the channel fluctuations of the users and scheduling transmissions to users when their instantaneous channel quality is near the peak. To increase this effect, additional channel fluctuation can be generated, e.g. by opportunistic beamforming. The core idea of opportunistic beamforming is to use a directive antenna system at the base station to generate random beam patterns which will be constant for a certain period until a new random beam pattern is chosen. As all cells act in the same way the interference that a mobile observes is based on the beam patterns in the cell that it is attached to (transmitting data to the mobile) and the beam patterns in the neighboring cells. As the cells vary their pattern from time to time the probability that a mobile observes good interference conditions is increased. The scheduling is based on the SINR (Signal to Interference-plus-Noise Ratio) that every mobile observes. Since the interference is usually modeled as noise, SINR is referred to as the SNR in the following.

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A reduced signaling scheme based on a new metric for opportunistic beamforming

Idea: Mohor Banerjee, DE-Bocholt; Sebastian Obermanns, DE-Bocholt; Malte Schmidt, DE-Bocholt

A fundamental characteristic of the wireless channel is the fading of the channel strength due to constructive and destructive interference between multipaths. An important means to cope with channel fading is the use of diversity. Multiuser diversity is a form of diversity inherent in a wireless network, provided by independent time-varying channels across the different users. The diversity benefit is exploited by tracking the channel fluctuations of the users and scheduling transmissions to users when their instantaneous channel quality is near the peak. To increase this effect, additional channel fluctuation can be generated, e.g. by opportunistic beamforming. The core idea of opportunistic beamforming is to use a directive antenna system at the base station to generate random beam patterns which will be constant for a certain period until a new random beam pattern is chosen. As all cells act in the same way the interference that a mobile observes is based on the beam patterns in the cell that it is attached to (transmitting data to the mobile) and the beam patterns in the neighboring cells. As the cells vary their pattern from time to time the probability that a mobile observes good interference conditions is increased. The scheduling is based on the SINR (Signal to Interference-plus-Noise Ratio) that every mobile observes. Since the interference is usually modeled as noise, SINR is referred to as the SNR in the following.

In order to use opportunistic beamforming, a proper signaling scheme is required because all terminals (or a pre-defined set of terminals) need to signal the information about the current SNR to the base station. Till now, no definite scheme exists which solves this problem in a suitable manner and ensures fairness to all the users.

It is proposed to use a signaling scheme that reduces the volume of feedback to the base station and thereby saves the bandwidth. In doing so, the multiuser diversity gains are not get lost. Furthermore, a new decision metric (SNRmetric) is introduced which guarantees equal fairness to all users.

The base station (BS) decides on a relative SNR threshold, above which it will schedule the users in a fair manner, and transmits this information to all the active users. The relative SNR threshold is defined as a certain ratio of the instantaneous SNR to the average SNR which is averaged over any arbitrary time scale. In the conventional proportional fair scheduler this time tc is the scheduling time window. The terminal keeps track of its average SNR and calculates its SNRmetric based on its instantaneous SNR level:

average ous

                 instantane =SNRSNRmetric SNR

The terminals compare their individual SNRmetric value with the SNR threshold received from the base station. Those who are above the threshold send their insta...