[show abstract][hide abstract] ABSTRACT: Third generation code-division multiple access (CDMA) systems propose to provide packet data service through a high speed shared channel with intelligent and fast scheduling at the base-stations. In the current approach base-stations schedule independently of other base-stations. We consider scheduling schemes in which scheduling decisions are made jointly for a cluster of cells thereby enhancing performance through interference avoidance and dynamic load balancing. We consider algorithms that assume complete knowledge of the channel quality information from each of the base-stations to the terminals at the centralized scheduler as well as a twotier scheduling strategy that assumes only the knowledge of the long term channel conditions at the centralized scheduler. We demonstrate that in the case of asymmetric traffic distribution, where load imbalance is most pronounced, significant throughput gains can be obtained while the gains in the symmetric case are modest. Since the load balancing is achieved through centralized scheduling, our scheme can adapt to time-varying traffic patterns dynamically.
[show abstract][hide abstract] ABSTRACT: Over the past few years, the design and performance of channel-aware scheduling strategies have attracted huge interest. In the present paper we examine a different notion of scheduling, namely coordination of transmissions among base stations, which has received little attention so far. The inter-cell coordination comprises two key elements: (i) interference avoidance; and (ii) load balancing. The interference avoidance involves coordinating the activity phases of interfering base stations so as to increase transmission rates. The load balancing aims at diverting traffic from heavily-loaded cells to lightly-loaded cells. We consider a dynamic scenario where users come and go over time as governed by the arrival and completion of random data transfers, and evaluate the potential capacity gains from inter-cell coordination in terms of the maximum amount of traffic that can be supported for a given spatial traffic pattern. Numerical experiments demonstrate that inter-cell scheduling may provide significant capacity gains, the relative contribution from interference avoidance vs. load balancing depending on the configuration and the degree of load imbalance in the network.
Wireless Conference 2005 - Next Generation Wireless and Mobile Communications and Services (European Wireless), 11th European; 05/2005
[show abstract][hide abstract] ABSTRACT: We investigate a wireless system of multiple cells, each having a downlink shared channel in support of high-speed packet
data services. In practice, such a system consists of hierarchically organized entities including a central server, Base Stations
(BSs), and Mobile Stations (MSs). Our goal is to improve global resource utilization and reduce regional congestion given
asymmetric arrivals and departures of mobile users, a goal requiring load balancing among multiple cells. For this purpose,
we propose a scalable cross-layer framework to coordinate packet-level scheduling, call-level cell-site selection and handoff,
and system-level cell coverage based on load, throughput, and channel measurements. In this framework, an opportunistic scheduling
algorithm—the weighted Alpha-Rule—exploits the gain of multiuser diversity in each cell independently, trading aggregate (mean) downlink throughput for fairness
and minimum rate guarantees among MSs. Each MS adapts to its channel dynamics and the load fluctuations in neighboring cells,
in accordance with MSs’ mobility or their arrival and departure, by initiating load-aware handoff and cell-site selection.
The central server adjusts schedulers of all cells to coordinate their coverage by prompting cell breathing or distributed
MS handoffs. Across the whole system, BSs and MSs constantly monitor their load, throughput, or channel quality in order to
facilitate the overall system coordination.
Our specific contributions in such a framework are highlighted by the minimum-rate guaranteed weighted Alpha-Rule scheduling, the load-aware MS handoff/cell-site selection, and the Media Access Control (MAC)-layer cell breathing. Our evaluations
show that the proposed framework can improve global resource utilization and load balancing, resulting in a smaller blocking
rate of MS arrivals without extra resources while the aggregate throughput remains roughly the same or improved at the hot-spots.
Our simulation tests also show that the coordinated system is robust to dynamic load fluctuations and is scalable to both
the system dimension and the size of MS population.
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