采用双向指标评价公众预防艾滋病知识知晓程度

目的 探讨使用“知晓率”和“误解率”双向指标在评价公众预防艾滋病知识知晓程度中的有效性。方法 调查山东、河北部分农村地区成年人群接受健康教育之前 (1 63 2人 )和之后 (1 2 5 6人 )在预防艾滋病的知识、态度 信念的变化及对艾滋病知识误解方面的变化。结果 1 应充分正视艾滋病预防知识的误解情况 ;2 接受多途径的传播信息使知晓率明显上升 ,除电视、周围人谈论外 ,接受了其他宣传途径所传播信息的人误解率明显小于未接受者 ;3 经过健康教育 ,导致知晓率上升、误解率下降 ,但知晓率改变的程度较误解率大 ,本研究认为误解与知晓并不是完全相反的对应关系 ,受更复杂的因素影响 ;4 艾滋病防治知识知晓能导致人们从正面认识艾滋病 ,倾向于增加积极态度、降低消极态度 ,而误解则导致人们从反面认识艾滋病 ,倾向于增加消极态度、降低积极态度。结论 建议健康教育工作者今后对人群艾滋病知识知晓程度的评价时 ,使用双重性指标 ,即“知晓率和误解率”。

BER Modified Decode-and-Forward Protocol for OFDM-Based Linear Multihop Networks

In orthogonal frequency division multiplexing （OFDM） based multihop communications, the conventional decodeand-forward （DF） relay scheme severely suffers from the error propagation problem. This drawback is serious in multihop networks as errors made by any relay node may fail the decoder at the destination in great chance. In this paper, we propose a bit error rate （BER） modified DF protocol （BMDF） which can be applied to systems where error correction channel coding and M-ary modulation are used. By modeling all links except the last one as a binary symmetric channel （BSC）, we derive a log likelihood ratio （LLR） modification function relying only on the accumulated BER of all previous links to be applied to the output of the soft demapper. Furthermore, to reduce the computational complexity and signaling overhead, the modification function is simplified from its original exponential expression and less BERs are delivered between nodes by making successive subcarriers share the same BER. In addition, for situations where the channel state information （CSI） of forward link is available, the proposed BMDF can be further enhanced by combining with subcarrier pairing （SP） and power allocation （PA）, where a sorted-channel gain SP scheme and a greedy PA algorithm are proposed. The simulation results verify thesignificant performance improvement to the conventional DF.

An Iterative Decoding Scheme for Davey-MacKay Construction

In the Davey-MacKay(DM) construction,the inner decoder treats unknown transmitted bits as random independent substitution errors. It limits the synchronization capability of the inner decoder, and thus weakens the error-correcting capability of the DM construction.In order to improve the performance of the DM construction, an iterative decoding scheme is proposed, which iteratively utilizes the more accurate estimates of transmitted codewords. In the proposed scheme, the estimated average bit error rates and the estimated low-density parity-check(LDPC) codewords from the outer decoder are fed back into the inner decoder to update the synchronization process. Simulation results show that the proposed iterative decoding scheme significantly outperforms the traditional DM construction.

Temporal Error Concealment Technique for MPEG-4 Video Streams

Concerning inter4v mode employed widely in MPEG-4 video, a new temporal error concealment scheme for MPEG-4 video sequences is proposed, which can selectively interpolate one or four motion vectors （MVs） for the missing macroblock （ MB ） according to the estimated MB coding mode. Performance of the proposed scheme is compared with the existing schemes with multiple testing sequences at different bit error rates. Experimental results show that the proposed algorithm can mask the impairments caused by transmission errors more efficiently than 0 MV and average MV methods by consuming more time for different bit error rates. It has an acceptable image quality close to that obtained by the selective motion vector matching （ SMVM ） algorithm, while taking less than half of cycles of operations. The proposed concealment scheme is suitable for low complexity video real-time implementations.

Generalised Closed-Form Symbol Error Rate Analysis for Orthogonal Space-Time Block Coded OFDM System

In this paper,the Symbol Error Rate(SER)performance for Orthogonal Space-Time Block Coded(OSTBC)Orthogonal Frequency Division Multiplexing(OFDM)systems over Nakagami-m fading channels is analysed.A novel closed-form SER expression is proposed,which incorporates the Gauss hypergeometric function and Appell hypergeometric function into the conventional Probability Density Function(PDF)approach.The proposed exact closed-form SER expression is a generalised solution since it perfectly captures OSTBCOFDM systems’performances when having different antenna configurations that employ various modulation schemes and which experience various fading conditions.Finally,Monte Carlo simulation results are provided to demonstrate the exact match between the simulation results and the proposed analytical expressions.