14687819
On finite precision implementation of low density parity check codes decoder
In this paper, we analyze the finite precision effects on the decoding performance of Gallager's low density parity check (LDPC) codes and develop optimal finite word lengths of variables as far as the tradeoffs between the performance and hardware complexity are concerned. We have found that 4 bits and 6 bits are adequate for representing the received data and extrinsic information, respectively. Simulation results indicate that the quantization scheme we have developed for the LDPC decoder is effective in approximating the infinite precision implementation.
28306753
Low hardware complexity parallel turbo decoder architecture
Turbo decoders inherently have low throughput and long latency because of iterative decoding. Parallel processing is a powerful technique for high-throughput applications but often comes with large hardware complexity penalties. In this paper, we present a generic low hardware complexity parallel turbo decoder architecture, which enables multiple soft-input soft-output (SISO) decoders to process one data frame simultaneously. It can achieve multiple times the throughput of a typical serial decoder with a small fraction of hardware overhead. The proposed architecture works for any type of random interleavers, which makes it extremely useful in practical applications where turbo interleave patterns are not free to design. Based on estimation, the illustrated low hardware complexity 2-level parallel turbo decoding architecture can achieve twice the throughput of a typical serial decoding architecture with less than 20% hardware overhead when applied to 3rd generation CDMA systems.
26353125
On the better protection of short-frame turbo codes
Protecting short data frames by turbo coding is a challenging task because of the small interleaver size and the need for transmission efficiency. In this letter, turbo-decoding-metrics aided short cyclic redundancy check codes are applied to novel tailbiting encoded trellis codes with a twofold purpose: to stop the iterative decoding processes to achieve low-power design and to reduce fractional coding-rate loss. Significant coding gains can be achieved by actually increasing the transmission rate with a negligible increase in power consumption. Performance improvement is demonstrated over additive white Gaussian noise channels. The savings is up to 21.4% for the transmission throughput and 21.5% for the energy consumption of the turbo decoder when frame size 49 is used.
47404061
Diversity and Multiplexing Tradeoff in General Fading Channels
The optimal tradeoff between diversity gain and multiplexing gain for multiple-inputmultiple-output (MIMO) channels has been studied recently under the independent and identically distributed (i.i.d.) Rayleigh-fading assumption. In this correspondence, this result is extended and the optimal tradeoff performance is derived for generalized fading channel conditions, including different fading types, nonidentical fading distributions, spatial correlation, and nonzero channel means. Our results include many known models as special cases and shed light on the effects of different channel parameters on the optimal tradeoff performance
9720590
Using the compiler to improve cache replacement decisions
Memory performance is increasingly determining microprocessor performance and technology trends are exacerbating this problem. Most architectures use set-associative caches with LRU replacement policies to combine fast access with relatively low miss rates. To improve replacement decisions in set-associative caches, we develop a new set of compiler algorithms that predict which data will and will not be reused and provide these hints to the architecture. We prove that the hints either match or improve hit rates over LRU. We describe a practical one-bit cache-line tag implementation of our algorithm, called evict-me. On a cache replacement, the architecture will replace a line for which the evict-me bit is set, or if none is set, it will use the LRU bits. We implement our compiler analysis and its output in the Scale compiler. On a variety of scientific programs, using the evict-me algorithm in both the level 1 and 2 caches improves simulated cycle times by up to 34% over the LRU policy by increasing hit rates. In addition, a combination of simple hardware prefetching and evict-me works together to further improve performance.
11332367
Quality-of-Service Routing for Supporting Multimedia Applications
Several new architectures have been developed for supporting multimedia applications such as digital video and audio. However, quality-of-service (QoS) routing is an important element that is still missing from these architectures. In this paper, we consider a number of issues in QoS routing. We first examine the basic problem of QoS routing, namely, finding a path that satisfies multiple constraints, and its implications on routing metric selection, and then present three path computation algorithms for source routing and for hop-by-hop routing.
14221801
An opto-VLSI based tunable fiber ring laser
We demonstrate a novel Opto-VLSI tunable fiber ring laser structure in which an Opto-VLSI processor driven by steering phase holograms dynamically selects the lasing wavelengths. A proof-of-concept tunable fiber ring laser which has a wavelength tuning range of more than 4 nm around 1530 nm and a side-mode suppression ratio more than 25 dB is demonstrated at room temperature. The output power of the lasing wavelengths can be controlled within 0.5 dB uniformity by reconfiguring the phase hologram of the Opto-VLSI processor. Dual-wavelength laser tuning is also experimentally demonstrated.
2647804
Extended DBP for (m, k)-Firm Based QoS
In this paper, an extended DBP (E_DBP) scheme is studied for (m,k)-firm constraint. The basic idea of the proposed algorithm takes into account the distance to exit a failure state, which is a symmetrical notion of distance to fall into a failure state in DBP. Quality of Service (QoS) in terms of dynamic failure and delay is evaluated. Simulation results reveal the effectiveness of E_DBP to provide better QoS.