Designing multihop wireless backhaul networks with delay guarantees

Abstract — As wireless access technologies improve in data rates, the problem focus is shifting towards providing adequate backhaul from the wireless access points to the Internet. Existing wired backhaul technologies such as copper wires running at DSL, T1, or T3 speeds can be expensive to install or lease, and are becoming a performance bottleneck as wireless access speeds increase. Longhaul, non-line-of-sight wireless technologies such as WiMAX (802.16d) hold the promise of enabling a high speed wireless backhaul as a cost-effective alternative. However, the biggest challenge in building a wireless backhaul is achieving guaranteed performance (throughput and delay) that is typically provided by a wired backhaul. This paper explores the problem of efficiently designing a multihop wireless backhaul to connect multiple wireless access points to a wired gateway. In particular, we provide a generalized link activation framework for scheduling packets over this wireless backhaul, such that any existing wireline scheduling policy can be implemented locally at each node of the wireless backhaul. We also present techniques for determining good interference-free routes within our scheduling framework, given the link rates and cross-link interference information. When a multihop wireline scheduler with worst case delay bounds (such as WFQ or Coordinated EDF) is implemented over the wireless backhaul, we show that our scheduling and routing framework guarantees approximately twice the delay of the corresponding wireline topology. Finally, we present simulation results to demonstrate the low delays achieved using our framework. I

Space-Efficient Scheduling for Parallel, Multithreaded Computations

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A Parallel, Multithreaded Decision Tree Builder

Parallelization has become a popular mechanism to speed up data classification tasks that deal with large amounts of data. This paper describes a high-level, fine-grained parallel formulation of a decision tree-based classifier for memory-resident datasets on SMPs. We exploit two levels of divide-and-conquer parallelism in the tree builder: at the outer level across the tree nodes, and at the inner level within each tree node. Lightweight Pthreads are used to express this highly irregular and dynamic parallelism in a natural manner. The task of scheduling the threads and balancing the load is left to a space-efficient Pthreads scheduler. Experimental results on large datasets indicate that the space and time performance of the tree builder scales well with both the data size and number of processors. This research is supported by ARPA Contract No. DABT63-96-C-0071. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes, notwithstanding any copyri..

Scheduling Threads for Low Space Requirement and Good Locality

The running time and memory requirement of a parallel program with dynamic, lightweight threads depends heavily on the underlying thread scheduler. In this paper, we present a simple, asynchronous, space-efficient scheduling algorithm for shared memory machines that combines the low scheduling overheads and good locality of work stealing with the low space requirements of depth-first schedulers. For a nested-parallel program with depth D and serial space requirement S 1 , we show that the expected space requirement is S 1 +O(K \Delta p \Delta D) on p processors. Here, K is a user-adjustable runtime parameter, which provides a tradeoff between running time and space requirement. Our algorithm achieves good locality and low scheduling overheads by automatically increasing the granularity of the work scheduled on each processor. We have implemented the new scheduling algorithm in the context of a native, user-level implementation of Posix standard threads or Pthreads, and evaluated its p..

Comparing Power Consumption of an SMT and a CMP DSP for Mobile Phone Workloads

In the DSP world, many media workloads have to perform a specific amount of work in a specific period of time. This observation led us to examine Simultaneous Multithreading (SMT) and Chip Multiprocessing (CMP) for a VLIW DSP architecture (specifically the Star*Core SC140), in conjunction with Frequency/Voltage scaling to decrease dynamic power consumption in next-generation wireless handsets. We study the resulting performance and power characteristics of the two approaches using simulation, compiled code, and realistic workloads that respect real-time constraints. We find that a multithreaded DSP can utilize the available functional units much more efficiently, performing as well as a non-multithreaded DSP but with substantial power savings. Power consumption can also be lowered by using a chip-multiprocesso

Admission control for multihop wireless backhaul networks with qos support

Abstract — Despite improvements in wireless access technologies such as 3G or 802.11x, ubiquitous data access has remained a challenge, mainly due to the lack of inexpensive, pervasive backhaul connections from access points to the Internet. With the recent WiMAX standard for high-speed, non-line-of-sight fixed wireless links, multihop wireless backhauls might now overcome this bottleneck. However an important remaining challenge is to provide rate and delay guarantees for customer connections similar to wired backhauls. We provide several schemes for performing admission control for connections with QoS requirements over a multihop wireless backhaul. This is the first work to address both rate and delay requirements for connections. Our admission control algorithms first construct appropriate tree-based topologies connecting wireless backhaul nodes to a wired gateway and then admit the best subset of connections while respecting their rate and delay requirements. Alternately, we admit all the connections with appropriate degradation of their QoS requirements. I

A Practical Comparison of N-Body Algorithms

This work compares three algorithms for the three dimensional N-body problem, the Barnes-Hut algorithm, Greengard's Fast Multipole Method(FMM), and the Parallel Multipole Tree Algorithm (PMTA) to determine which of the algorithms performs best in practice. Although FMM has a better asymptotic running time (O(N ) instead of O(N log N ) for uniform distributions), the algorithm is more complicated and it is not immediately clear above what values of N it performs better in practice. We studied the dependence of accuracy on the variable parameters `, p and ff, and then compared the floating point operation counts of the three algorithms at similar levels of accuracy, for both charged and uncharged random distributions. At a high level of accuracy (RMS-error ß 10 \Gamma5 ), the FMM did the least number of operations for N ? 10 4 , assuming both charged and uncharged distributions of points. At a lower level of accuracy, (RMS-error ß 10 \Gamma3 ) for uncharged distributions, the FMM d..