﻿ 基于冲击滤波器的EBPSK软解调研究 Research on EBPSK Soft Demodulation Based on Impact Filter

Hans Journal of Wireless Communications
Vol.05 No.06(2015), Article ID:16483,8 pages
10.12677/HJWC.2015.56016

Research on EBPSK Soft Demodulation Based on Impact Filter

Qi Hu, Lenan Wu

Radio Engineering Department, Southeast University, Nanjing Jiangsu

Received: Nov. 6th, 2015; accepted: Nov. 27th, 2015; published: Dec. 8th, 2015

ABSTRACT

This paper researches the possibility and performance of EBPSK soft demodulation based on impact filter. We use impact filter to demodulate EBPSK signals generally. Because of the impact filter’s nonlinear character, it is hard to implement EBPSK soft demodulation. Referring to BPSK soft demodulation in Gaussian channel, this paper puts forward the theoretical soft information formula which is the critical point of soft demodulation, and verifies the rationality of the formula. Chase-3 algorithm is used to simulate this soft demodulation scheme and the simulation results show that soft demodulation scheme increases 0.5 dB compared with hard demodulation.

Keywords:EBPSK, Impact Filter, Soft Demodulation, Chase Algorithm

1. 引言

2. 基本原理

2.1. EBPSK调制

EBPSK的统一表达式[1] 如下：

(1)

2.2. 冲击滤波器

(2)

2.3. EBPSK信号通过冲击滤波器

(3)

(4)

(5)

(6)

(7)

(8)

1) 在范围内：

(9)

2) 在范围内：

(10)

(11)

(12)

(a)(b)

Figure 1. EBPSK waveform and filter output waveform

(13)

(14)

(15)

2.4. Chase-3软解调算法

Chase算法有3种，这里选用复杂度最低的Chase-3算法。其实现步骤如下：

(a) 信号0 (b) 信号1

Figure 2. Probability density function of EBPSK signals after filter

Chase-2算法是对上面的改进，它产生更大的候选码字列表，在这个算法里，z的个最不可靠位置所有可能错误的集合E用来修正z。

Chase-1算法是通过取补硬判决接收序列z中位所有可能组合而产生的候选码字列表。

3. 基于幅度的软解调算法的可行性

3.1. 软解调原理

(16)

(17)

Figure 3. Relation between LLR and magnitude

3.2. 幅度作为软判决度量的可行性分析

(18)

4. 仿真结果与结论

1) 硬判决得到序列z，并计算每一位的可信度。

2) 按照Chase-3里的方法修正z，得到试探序列集合T。

3) 对修正后的序列进行BCH解码，并计算其软判决度量C的大小。

4) C中最小的值对应的序列即为解调结果。

5) 计算误码率。

Figure 4. Relation between errors and reliability

Figure 5. BER of EPBSK soft demodulation and hard demodulation

5. 结束语

Research on EBPSK Soft Demodulation Based on Impact Filter[J]. 无线通信, 2015, 05(06): 111-118. http://dx.doi.org/10.12677/HJWC.2015.56016

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