Daniel Yellin

Linear Precoding Bounds for Wyner-Type Cellular Networks With Limited Base-Station Cooperation and Dynamic Clustering

This work studies the achievable average data rate in the downlink of a Wyner-type linear cellular network with limited cooperation and linear precoders. We derive upper and lower bounds on the achievable average data rate subject to an average power constraint. The bounds show that even a small number of cooperating base stations applying suboptimal (linear) precoding can approach optimal performance, and significantly increase the average user data rates as compared to those achievable with noncooperating cellular systems. We highlight the importance of dynamic clustering and of base station (BS) silencing. Dynamic clustering allows the system to build clusters that benefit some users at the expense of others, and then shifts the priority between the users. Such a scheme results in higher average rates for all users, while meeting some level of fairness. BS silencing is shown to be important for limited cooperation networks in the high SNR regime. Silencing is a simple and efficient way to reduce the interference (and hence increase the user rates) without increasing the number of cooperating BSs. The theoretical analysis is accompanied by several numerical examples in selected scenarios.

Uplink downlink balancing using variable feedback rates

The broadcast MIMO channel have gained much attention in recent years, and in particular in the context of cooperative multi cell transmission in cellular networks. Broadcast MIMO techniques can signifcantly increase the capacity in the downlink of cellular networks, at the price of channel state information (CSI) feedback from the mobiles. Thus, it creates a mechanism that can tradeoff uplink rate to downlink rate. In this work we quantify this tradeoff between the feedback rate (over the uplink) and the downlink rate. We show that uplink rate can be exchanged to downlink rate with a constant exchange ratio. This exchange ratio is an increasing function of the channel coherence time, and a decreasing function of the number of measured BSs. We also show that devoting a constant ratio of the uplink to CSI feedback can increase the downlink multiplexing gain continuously from 0 to 1. This capability to control the balance between the uplink and downlink rates is very important in cellular networks, where the operators need to respond to continuously changing user demands.

A Lower Bound on the Data Rate of Dirty Paper Coding in General Noise and Interference

Dirty paper coding (DPC) allows a transmitter to send information to a receiver in the presence of interference that is known (noncausally) to the transmitter. The original version of DPC was derived for the case where the noise and the interference are statistically independent Gaussian random sequences. More recent works extended this approach to the case where the noise and the interference are mutually independent and at least one of them is Gaussian. In this letter, we further extend the DPC scheme by relaxing the Gaussian and statistical independence assumptions. We provide lower bounds on the achievable data rates in a DPC setting for the case of possibly dependent noise, interference, and input signals. Moreover, the interference and noise terms are allowed to have arbitrary probability distributions. The bounds are relatively simple, are phrased in terms of second-order statistics, and are tight when the actual noise distribution is close to Gaussian.

Linear precoding bounds for the Wyner cellular channel model with limited cooperation

We present upper and lower bounds on the achievable average user data rates in the downlink of a one-dimensional Wyner cellular channel model when limited cooperation and linear precoding are employed. These bounds show that the user data rates can be dramatically increased compared to those achievable with non-cooperating cellular systems. Furthermore, the bounds show that near optimal performance can be achieved with a small number of cooperating base stations (BSs) and a simple to implement linear precoding scheme.