The single-carrier block transmission（SCBT）,a.k.a.,single-carrier frequency-domain equalization（SC-FDE）,is being considered as an option technique for the wireless personal area network（WPAN） operating at 60 GHz...The single-carrier block transmission（SCBT）,a.k.a.,single-carrier frequency-domain equalization（SC-FDE）,is being considered as an option technique for the wireless personal area network（WPAN） operating at 60 GHz.It is found that for residential environment,in non-line-of-sight（NLOS） multi-path channels,the SCBT is much more effective to combat the inter-symbol interference（ISI） compared with orthogonal frequency division multiplexing（OFDM）.Low-density parity-check（LDPC） codes are a class of linear block codes which provide near capacity performance on a large collection of data transmission and storage channels while simultaneously admitting implementable decoders.To facilitate using LDPC codes for SCBT system,a new log-likelihood ratio（LLR） calculation method is proposed based on pilot symbols（PS）.Golay Sequences whose sum autocorrelation has a unique peak and zero sidelobe are used for creating the PS.The position and length of the PS are not fixed in the data blocks.The simulation results show that the proposed method can significantly improve the LDPC decoding performance in SCBT system.This is very promising to support ultra high-data-rate wireless transmission.展开更多
Game-tree search plays an important role in the field of Artificial Intelligence （AI）. In this paper, we characterize one parallel game-tree search workload in chess： the latest version of Crafty, a state of art pr...Game-tree search plays an important role in the field of Artificial Intelligence （AI）. In this paper, we characterize one parallel game-tree search workload in chess： the latest version of Crafty, a state of art program, on two Intel Xeon shared-memory multiprocessor systems. Our analysis shows that Crafty is latency-sensitive and the hash-table and dynamic tree splitting used in Crafty cause large scalability penalties. They consume 35%-50% of the running time on the 4-way system. Furthermore, Crafty is not bandwidth-limited.展开更多
In cognitive radio systems,the design of spectrum sensing has to face the challenges of radio sensitivity and wide-band frequency agility. It is difficult for a single cognitive user to achieve timely and accurate wid...In cognitive radio systems,the design of spectrum sensing has to face the challenges of radio sensitivity and wide-band frequency agility. It is difficult for a single cognitive user to achieve timely and accurate wide-band spectrum sensing because of hardware limitations. However,cooperation among cognitive users may provide a way to do so. In this paper,we consider such a cooperative wide-band spectrum sensing problem with each of the cognitive users able to imperfectly sense only a small portion of spectrum at a time. The goal is to maximize the average throughput of the cognitive network,given the primary network's collision probability thresholds in each spectrum sub-band. The solution answers the essential questions:to what extent should each cognitive user cooperate with others and which part of the spectrum should the user choose to sense? An exhaustive search is used to find the optimal solution and a heuristic cooperative sensing algorithm is proposed to simplify the computational com-plexity. Inspired by this optimization problem,two practical cooperative sensing strategies are then presented for the centralized and distributed cognitive network respectively. Simulation results are given to demonstrate the promising performance of our proposed algorithm and strategies.展开更多
Fractional frequency reuse （FFR） is an effective technique to mitigate co-channel interference in orthogonal frequency division multiple access （OFDMA）-based broadband cellular systems.In this paper,we present a g...Fractional frequency reuse （FFR） is an effective technique to mitigate co-channel interference in orthogonal frequency division multiple access （OFDMA）-based broadband cellular systems.In this paper,we present a generalized model for FFR under which all existing FFR schemes can be considered as its special cases.Additionally,quality factor has been proposed to indicate the quality of the subband.An interesting conclusion can be drawn that,as the power ratio in FFR is adjusted continuously,the corresponding quality factor varies smoothly.Subsequently,simulation is conducted based on worldwide interoperability for microwave access （WiMAX）,and the result agrees well with our theoretical analysis.Finally,an effective range for power ratio is presented,which is very instructive to practical system design.展开更多
Stride prefetching is recognized as an important technique to improve memory access performance. The prior work usually profiles and/or analyzes the program behavior offline, and uses the identified stride patterns to...Stride prefetching is recognized as an important technique to improve memory access performance. The prior work usually profiles and/or analyzes the program behavior offline, and uses the identified stride patterns to guide the compilation process by injecting the prefetch instructions at appropriate places. There are some researches trying to enable stride prefetching in runtime systems with online profiling, but they either cannot discover cross-procedural prefetch opportunity, or require special supports in hardware or garbage collection. In this paper, we present a prefetch engine for JVM （Java Virtual Machine）. It firstly identifies the candidate load operations during just-in-time （JIT） compilation, and then instruments the compiled code to profile the addresses of those loads. The runtime profile is collected in a trace buffer, which triggers a prefetch controller upon a protection fault. The prefetch controller analyzes the trace to discover any stride patterns, then modifies the compiled code to inject the prefetch instructions in place of the instrumentations. One of the major advantages of this engine is that, it can detect striding loads in any virtual code places for both regular and irregular code, not being limited with plain loop or procedure scopes. Actually we found the cross-procedural patterns take about 30% of all the prefetchings in the representative Java benchmarks. Another major advantage of the engine is that it has runtime overhead much smaller （the maximal is less than 4.0%） than the benefits it brings. Our evaluation with Apache Harmony JVM shows that the engine can achieve an average 6.2% speed-up with SPECJVM98 and DaCapo on Intel Pentium 4 platform, in spite of the runtime overhead.展开更多
基金supported by the National Natural Science Foundation of China (60572093)Specialized Research Fund for the DoctoralProgram of Higher Education (20050004016)
文摘The single-carrier block transmission（SCBT）,a.k.a.,single-carrier frequency-domain equalization（SC-FDE）,is being considered as an option technique for the wireless personal area network（WPAN） operating at 60 GHz.It is found that for residential environment,in non-line-of-sight（NLOS） multi-path channels,the SCBT is much more effective to combat the inter-symbol interference（ISI） compared with orthogonal frequency division multiplexing（OFDM）.Low-density parity-check（LDPC） codes are a class of linear block codes which provide near capacity performance on a large collection of data transmission and storage channels while simultaneously admitting implementable decoders.To facilitate using LDPC codes for SCBT system,a new log-likelihood ratio（LLR） calculation method is proposed based on pilot symbols（PS）.Golay Sequences whose sum autocorrelation has a unique peak and zero sidelobe are used for creating the PS.The position and length of the PS are not fixed in the data blocks.The simulation results show that the proposed method can significantly improve the LDPC decoding performance in SCBT system.This is very promising to support ultra high-data-rate wireless transmission.
文摘Game-tree search plays an important role in the field of Artificial Intelligence （AI）. In this paper, we characterize one parallel game-tree search workload in chess： the latest version of Crafty, a state of art program, on two Intel Xeon shared-memory multiprocessor systems. Our analysis shows that Crafty is latency-sensitive and the hash-table and dynamic tree splitting used in Crafty cause large scalability penalties. They consume 35%-50% of the running time on the 4-way system. Furthermore, Crafty is not bandwidth-limited.
基金supported in part by the National Basic Research Program (973) of China (No. 2009CB320405)the National Natural Science Foundation of China (No. 60972057)the National High-Tech Research and Development Program (863) of China (No. 2007AA 01Z257)
文摘In cognitive radio systems,the design of spectrum sensing has to face the challenges of radio sensitivity and wide-band frequency agility. It is difficult for a single cognitive user to achieve timely and accurate wide-band spectrum sensing because of hardware limitations. However,cooperation among cognitive users may provide a way to do so. In this paper,we consider such a cooperative wide-band spectrum sensing problem with each of the cognitive users able to imperfectly sense only a small portion of spectrum at a time. The goal is to maximize the average throughput of the cognitive network,given the primary network's collision probability thresholds in each spectrum sub-band. The solution answers the essential questions:to what extent should each cognitive user cooperate with others and which part of the spectrum should the user choose to sense? An exhaustive search is used to find the optimal solution and a heuristic cooperative sensing algorithm is proposed to simplify the computational com-plexity. Inspired by this optimization problem,two practical cooperative sensing strategies are then presented for the centralized and distributed cognitive network respectively. Simulation results are given to demonstrate the promising performance of our proposed algorithm and strategies.
基金supported by the National Natural Science Foundation of China (60872049, 60871042)the Hi-Tech Research and Development Program of China (2007AA10Z235)the Teaching and Research Finances for the Returned Overseas Chinese Scholars
文摘Fractional frequency reuse （FFR） is an effective technique to mitigate co-channel interference in orthogonal frequency division multiple access （OFDMA）-based broadband cellular systems.In this paper,we present a generalized model for FFR under which all existing FFR schemes can be considered as its special cases.Additionally,quality factor has been proposed to indicate the quality of the subband.An interesting conclusion can be drawn that,as the power ratio in FFR is adjusted continuously,the corresponding quality factor varies smoothly.Subsequently,simulation is conducted based on worldwide interoperability for microwave access （WiMAX）,and the result agrees well with our theoretical analysis.Finally,an effective range for power ratio is presented,which is very instructive to practical system design.
基金the National Natural Science Foundation of China under Grant Nos.60673146,60603049,60736012,and 60703017the National High Technology Development 863 Program of China under Grant No.2006AA010201 and No.2007AA01Z114the National Basic Research Program of China under Grant No.2005CB321601.
文摘Stride prefetching is recognized as an important technique to improve memory access performance. The prior work usually profiles and/or analyzes the program behavior offline, and uses the identified stride patterns to guide the compilation process by injecting the prefetch instructions at appropriate places. There are some researches trying to enable stride prefetching in runtime systems with online profiling, but they either cannot discover cross-procedural prefetch opportunity, or require special supports in hardware or garbage collection. In this paper, we present a prefetch engine for JVM （Java Virtual Machine）. It firstly identifies the candidate load operations during just-in-time （JIT） compilation, and then instruments the compiled code to profile the addresses of those loads. The runtime profile is collected in a trace buffer, which triggers a prefetch controller upon a protection fault. The prefetch controller analyzes the trace to discover any stride patterns, then modifies the compiled code to inject the prefetch instructions in place of the instrumentations. One of the major advantages of this engine is that, it can detect striding loads in any virtual code places for both regular and irregular code, not being limited with plain loop or procedure scopes. Actually we found the cross-procedural patterns take about 30% of all the prefetchings in the representative Java benchmarks. Another major advantage of the engine is that it has runtime overhead much smaller （the maximal is less than 4.0%） than the benefits it brings. Our evaluation with Apache Harmony JVM shows that the engine can achieve an average 6.2% speed-up with SPECJVM98 and DaCapo on Intel Pentium 4 platform, in spite of the runtime overhead.
