Bidirectional iterative ISI canceller for high-rate DSSS/CCK communications

This paper proposes a new RAKE receiver incorporated with a bidirectional iterative intersymbol interference (ISI) canceller in order to reinforce multipath robustness of high-rate direct-sequence spread-spectrum complementary code keying (DSSS/CCK) systems. The proposed RAKE receiver first combines multipath signal components through a channel matched filter (CMF) and removes postcursor-ISI by employing a codeword decision feedback equalizer (DFE). Then, a CCK codeword detector tentatively determines the current CCK codeword symbol and reuses it to subtract precursor-ISI from the previous symbol. Therefore, the ultimate symbol decision is made using the delayed signal with both postcursor-ISI and precursor-ISI cancelled. The detection performance can be more improved through an iterative refinement processing between the postcursor and the precursor components. Simulation results exhibit a significantly improved error rate performance of the proposed receiver compared with that of the legacy RAKE receiver employing only a postcursor DFE. The additional cost for realization of the proposed receiver is one symbol decision delay and reuse complexity of the DFE and the codeword detector.     

Near-optimal decoding for coded and power-controlled DS-CDMA downlink

We first present the traditional decoding approach that employs the common pilot-channel-based maximal ratio combining and the Viterbi or iterative decoding cannot achieve the optimal error-rate performance for downlink direct-sequence code-division multiple-access (CDMA) signals when a fast power control technique is applied together with a convolutional or turbo coding. Then, as an efficient method to realize a nearly optimal decoding, we propose a branch metric power readjustment (BMPR) technique, where the downlink power control command generated by the mobile station is used not only to adjust the base station power in the transmitter side, but also to readjust the decoder input branch metric power in the receiver side. Numerical results show that the BMPR technique applied to the IMT-2000 wideband-CDMA system can improve the transmit power utilization by up to 0.4 dB for the block-error rate of 10/sup -2/.     

OCDD/CDMA: a new DS/CDMA with orthonormal code diversity detection

The paper presents a new spread spectrum communication system called orthonormal code diversity detection (OCDD)/CDMA system based on the novel concept of orthonormal-basis diversity which is a generalization of the existing spread spectrum diversity concepts such as path diversity and frequency diversity. The OCDD/CDMA system is similar to the conventional DS/CDMA system in the transmitter structure, but is different in the receiver structure as it employs the extended orthonormal basis-function set which is the union of the Walsh basis-functions multiplied by the PN sequences and, optionally, their delayed replicas. The received signal is matched to the extended basis functions, and the matched signal components are combined together after individual channel compensation. The proposed OCDD/CDMA system exhibits the bit error performance which is much improved over the conventional DS/CDMA system using maximal ratio combing. In addition, it is robust to the chip timing error, which becomes more crucial in the future DS/CDMA systems having a higher data rate and smaller chip interval. From the simulation results, we confirm that the OCDD/CDMA system is a unique spread spectrum communication technique that can effectively increase the diversity utilization in the slowly fading channel, overcoming the inherent problems in the DS/CDMA and OFDM/CDMA systems     

Distributed sample acquisition-based fast cell search in inter-cellasynchronous DS/CDMA systems

We introduce a fast fell-search scheme based on the distributed sample acquisition (DSA) technique for inter-cell asynchronous DS/CDMA systems. The proposed DSA scheme enables the long-code acquisition extremely fast even without employing any passive matched filter which used to dominate synchronization circuit complexity in asynchronous DS/CDMA systems. In the DSA-based asynchronous DS/CDMA system, each base station spreads its DQPSK-modulated long-code generator information with an assigned short-period igniter sequence, and broadcasts it as a common pilot signal. A mobile station first identifies and acquires the igniter sequence of the cell group currently located, then detects the conveyed long-code generator information by despreading the acquired igniter sequence, thereby identifying and synchronizing the long-code of the current cell. The mean acquisition time of this proposed DSA-based inter-cell asynchronous DS/CDMA system, evaluated under the assumption that each of 512 cell-specific long-codes is a 10-ms segment (38400-chips for the chip rates of 3.84 Mchips/s) of complex Gold codes of period 2¹⁸-1 and the igniter sequence (or, group code) set is composed of 7 complex orthogonal Gold codes of period 256, turned out even shorter than that of the inter-cell synchronous DS/CDMA systems employing the conventional serial search method. Furthermore, simulation results showed that the DSA scheme employing a passive matched filter is much superior in terms of acquisition time and robustness, to the 3GPP W-CDMA synchronization scheme having comparable complexity     

PDSA: parallel distributed sample acquisition for M-ary DS/CDMAsystem

We propose a parallel distributed sample acquisition (PDSA) scheme applicable to a direct-sequence code-division multiple-access (DS/CDMA) system employing M-ary signaling for data transmission. While the primitive distributed sample acquisition scheme can be employed only for the binary signaling systems which transmit 1 bit per symbol, the proposed PDSA scheme extends its applicability to the general signaling systems allowing multibit transmission per symbol. The proposed PDSA technique can also be applied to fast acquisition of the scrambling code in multicarrier DS/CDMA cellular systems with a slight modification of the transceiver circuitry     

DSA techniques for fast and robust acquisition of DS/CDMA scrambling codes

This article introduces the key concepts, organization, and operations of distributed sample-based acquisition (DSA) systems, which have previously been introduced for fast and robust synchronization of the long-period scrambling codes in DS/CDMA environments. In DSA systems, the transmitter samples and sends the state of its main sequence generator, or main shift register generator (SRG), in a distributed manner over the short-period igniter sequence, and the receiver detects and applies the state samples to correct the state of its main SRG, thereby acquiring SRG synchronization after a round of state reception. Acquisition performance of DSA techniques is extremely fast and robust compared to typical correlation-based acquisition techniques of comparable complexity. This article discusses the operation and performance of DSA techniques in the DS/CDMA communication environment as well as their applications to intercell synchronous and asynchronous cellular systems.     

Adaptive multi-node incremental relaying for hybrid-ARQ in AF relay networks

This paper proposes an adaptive multi-node incremental relaying technique in cooperative communications with amplify-and-forward (AF) relays. In order to reduce the excessive burden of MRC with all diversity paths at the destination node, the destination node decides if it combines signals over the first Ν(< Κ) time slots/frames or over all of the Κ times slots, where Κis the number of relay nodes. Our analytical and simulation results show that the proposed adaptive multi-node incremental relaying outperforms the conventional MRC in terms of outage probability in AF based cooperative communications since the proposed scheme effectively reduces the spectral efficiency loss. Our asymptotic analysis also shows that the proposed adaptive multi-node incremental relaying achieves full diversity order Κ+ 1.     

DSA: a distributed sample-based fast DS/CDMA acquisition technique

We propose a new acquisition scheme called distributed sample acquisition (DSA) which is applicable to the direct-sequence code-division multiple-access (DS/CDMA) system with a long-period pseudonoise (PN) sequence. The proposed scheme lays its foundations on an auxiliary PN sequence called the igniter sequence, which has relatively short period, and the distributed sample scrambling (DSS) technique previously developed for the asynchronous transfer mode cell transmission. In the DSA scheme, acquisition is done in three steps. First, the igniter sequence is synchronized, which normally takes a very short time due to its short period. Second, the state samples of the long-period PN sequence generator in the transmitter, which are conveyed to the receiver over the igniter sequence stream, are determined out of the synchronized igniter sequence. Third, the long-period PN sequence is synchronized by applying the state samples to the DSS receiver. Since the operation of each step takes a very short time, the overall acquisition is done very quickly. We analyze the acquisition time performance of the proposed scheme by taking the transform domain approach, confirming that the resulting mean acquisition time is dramatically reduced. If compared with the existing serial-search scheme, the DSA scheme can perform acquisition about 100 times faster when the period of the PN sequence is 2¹⁵-1. None the less, the additional circuit complexity for its implementation is very small     

Quantitative microbiological profiles of brown rice and germinated brown rice

Among health conscious people, brown rice (BR) and germinated brown rice (GBR) are increasingly more popular for consumption in Korea because their nutritional values are greater than those of ordinary white rice (WR). The overall microbial counts for BR were higher than those for WR and those of GBR were higher than those of BR. Interestingly, the lactic acid bacteria (LAB) counts in GBR increased markedly and their selected representatives were Weissella confusa, Pediococcus pentosaceus, and Lactobacillus fermentum. To our knowledge, this is the first attempt to enumerate and compare LAB loads on WR, BR, and GBR.     

Lease-based consistency schemes in the web environment

There are many methods to maintain consistency in the distributed computing environment. Ideally, efficient schemes for maintaining consistency should take into account the following factors: lease duration of replicated data, data access pattern and system parameters. One method used to supply strong consistency in the web environment is the lease method. During the proxy’s lease time from a web server, the web server can notify the modification to the proxy by invalidation or update. In this paper, we analyze lease protocol performance by the varying update/invalidation scheme, lease duration and read rates. By using these analyses, we can choose the adaptive lease time and proper protocol (invalidation or update scheme of the modification for each proxy in the web environment). As the number of proxies for web caching increases exponentially, a more efficient method for maintaining consistency needs to be designed. We also present three-tier hierarchies on which each group and node independently and adaptively choose the proper lease time and protocol for each proxy cache. These classifications of the scheme make proxy caching adaptive to client access pattern and system parameters.