【作者】 王磊；

【导师】 徐大专；

【作者基本信息】 南京航空航天大学 ， 通信与信息系统， 2012， 博士

【摘要】 1974年Massey根据Shannon信息论最早证明了若将编码与调制作为一个整体进行最佳设计可以大大地改善系统性能。1982年Ungerboeck提出了著名的网格编码调制(TCM)技术。TCM技术的提出被公认为是自Shannon提出信息论以来通信领域的一个里程碑。但TCM在衰落信道中的性能并不理想。比特交织编码调制(BICM)技术通过在编码器和调制器之间插入比特交织器提高了系统在衰落信道下的分集度并增强了系统设计的灵活性。近年来，BICM由于频谱利用率高、在衰落信道中性能优异等优点逐渐作为当今通信系统中的主流技术，如ETSI制定的DVB-T、DAB和DRM；3GPP制定WCDMA的增强版本HSPA及其演进版本LTE；IEEE制定的802.11和802.16等系列标准。为了减小由于编码器和调制器级联后的性能损失，BICM的解调器通过软解调为译码器提供每个比特的度量值。虽然根据最大似然(ML)准则得出的比特度量值具有最优的系统性能，但在高阶调制中，ML比特度量值的计算非常复杂。因此Max-Log是最常用的比特度量值计算方法。为了适应自适应调制的需求并简化高阶调制时的计算复杂度，本论文的主要工作为对各种调制方式下的比特度量值的近似计算进行研究。在无限长交织器假设下，本文首先给出了BICM系统传统的独立并行子信道模型，并分析了信道容量、截止速率和误码率性能限。针对实际应用中有限长交织器的情况，引入了非匹配译码模型及其广义互信息(GMI)分析方法。在此基础上，本文证明了GMI的凸函数性质，系统地给出了BICM系统的GMI计算方法，得到了在非匹配译码模型中性能的上限，为比较现有的各种BICM系统性能提供了依据。本文针对格雷标号方式下的PSK调制，提出一种低复杂度的比特度量计算方法。本文首先用三角函数给出格雷码各个比特的取值表达式，在此基础上推导出各个比特度量值之间的递推关系，利用递推可将所有比特统一转换为最高比特的度量值来计算，然后本文再给出最高比特度量值的计算方法。由于相邻比特间的递推关系与调制阶数无关，因此该方法不受调制阶数的影响，可用于自适应调制系统，且在高阶调制下具有很小的计算复杂度。本文以广义互信息和系统误码率为衡量指标，表明该简化方法在AWGN信道和衰落信道中的性能损失很小。本文给出ASK和QAM调制方式的低复杂度比特度量值计算方法。该方法仍然利用递推将所有比特的度量值转换为最高比特的度量值来计算。由于最高比特的度量值函数是该方法的关键，因此本文给出了三种近似函数，其中分段线性函数的性能和Max-Log完全相同，非线性函数的和Max-Log各有优劣，然后根据前两个近似函数的优缺点，给出了性能更优的混合近似函数。通过分析和仿真表明，本文所提的方法不仅计算复杂度低，且其性能和Max-Log非常接近。若采用混合近似函数，该方法的性能将超过Max-Log。本文对阶数为22k+1的调制方式的比特度量值计算进行了研究。由于在BICM系统中，采用Cross-QAM星座的32-QAM和128-QAM是两种最常用的方式。本文针对这两种调制方式，提出来一种使用区域划分的线性比特度量值函数，即比特度量值函数近似为分区域线性函数。该方法先根据Max-Log度量值的取值将复平面划分为多个区域，再根据区域边界判决简单和近似误差小的原则进行两次区域合并，其中第2次区域合并会引入部分一定计算误差，在实际应用中，可根据系统的实际需要进行取舍。该方法也可以进一步应用到阶数更高的调制方式。通过分析仿真表明，该方法可大大降低计算负担且性能优异。更多还原

【Abstract】 According to Shannon information theory, Massey proved that the system performance can be improved greatly by optimizing channel coding and modulation togather in1974. Then Ungerboeck proposed the famous Trellis coded modulation (TCM) technique in1982. TCM is considering as a milestone in the field of communications after Shannon information theory. However, the performance of TCM is not robust in fading channel. Bit-interleaved coded modulation (BICM) technique inserts the bit interleaver between coder and modulator to improve the degree of diversity in fading channel which can improve the performance of BICM system in fading channel and enhance the flexibility of system. In the recent years, bit-interleaved coded modulation (BICM) has become the de facto scheme of modern communication systems due to its flexibility, high spectrum efficiency and robust performance over fading channels, such as DVB-T, DAB, DRM, HSDPA,802.11,802.16and LTE etc..In order to reduce the performance loss for cascading encoder and modulator, the soft bit metrics are computed by the demodulator and provided to the the soft-decision decoder. The optimal bit metrics for BICM systems are maximum likelihood (ML) bit metrics, but the calculation for ML bit metrics are too complicated to implication in high-order modulation. So Max-Log is the most common bit metric generation method in practice. To meet the need of adaptive modulation in moderm communication systems, the dissertation researchs the methods of bit metric calculation for some modulation types and proposed some general bit metric generation approaches with low complexity and similar even better performance than Max-Log.Firstly, the conventional paralell sub-channel model and the new dismatched decoding model are described for BICM systems. Then the generalized mutual information (GMI) is introduced. To make the GMI as a performance measurement for different bit metrics, this dissertation derived some properties of GMI. The convex property simplifies the complexity to computer GMI. The relationship of the bit metric and GMI is further elaborated.This dissertation proposes a low complexity bit metirc calculation method for PSK signaling with Gray labeling. This approach converts all bit metrics to the bit metric of most significant bit (MSB) by recursion. The complexity of the method is very low compared to Max-Log bit metric. Because of the recursive formula is unrelated to modulation order, the proposed method can be used for any modulated signals of PSK and is very suitable for adaptive modulation systems. The GMI and bit error rate (BER) are used to measure the performance of this simplifed bit metrics. The simulation results demonstrate this method has similar performance compared to ML bit metirc over AWGN channel and fading channels.This dissertation extends the above method to ASK and QAM signals which is more common in practice for high-order modulation. This method is based on the bit metric calculation function of MSB by recursion. For the importance of the metric function of the MSB, this dissertation derived non-linear and peicewise linear approximate functions and analyse their performances in BICM systems. The the mixed apprximate function is derived which has better performance the Max-Log. When the number of bits per symbol is odd, the Cross-QAM and pseudo-Gray is the best constellation and labeling type. In BICM systems,32-QAM and128-QAM are the most common modulation types. In this dissertation, a simplified bit generation method is proposed base on region dividing. The complex plane is divided to some regions by Max-Log bit metrics firstly. Then we merged these regions by its bit metric generation function which can make regular region boundary.更多还原